Fix spelling

CID 75872 (#3-2 of 3): Pointer to local outside scope (RETURN_LOCAL)
38. use_invalid: Using p, which points to an out-of-scope variable buf.

The following code crashes without this change:

    def a
      [1].each do
        [2].each do
          [3].each do
            raise "XXX"
          end
        end
      end
    end

    begin
      a
    rescue => exception
      GC.start
      exception.backtrace
    end

GDB backtrace:

    Program received signal SIGSEGV, Segmentation fault.
    strlen () at ../sysdeps/x86_64/strlen.S:106
    106	../sysdeps/x86_64/strlen.S: No such file or directory.
    (gdb) bt
    #0  strlen () at ../sysdeps/x86_64/strlen.S:106
    #1  0x00000000004252cd in mrb_str_new_cstr (mrb=0x69f010,
        p=0x101 <error: Cannot access memory at address 0x101>)
        at mruby/src/string.c:290
    #2  0x00000000004183fe in get_backtrace_i (mrb=0x69f010, loc=0x7fffffffd940,
        data=0x6a7410) at mruby/src/backtrace.c:72
    #3  0x0000000000418793 in output_backtrace (mrb=0x69f010, ciidx=8,
        pc0=0x71940c, func=0x4183af <get_backtrace_i>, data=0x6a7410)
        at mruby/src/backtrace.c:140
    #4  0x0000000000418862 in exc_output_backtrace (mrb=0x69f010, exc=0x6a5be0,
        func=0x4183af <get_backtrace_i>, stream=0x6a7410)
        at mruby/src/backtrace.c:157
    #5  0x000000000041894c in mrb_exc_backtrace (mrb=0x69f010, self=...)
        at mruby/src/backtrace.c:199
    #6  0x000000000040dbaf in mrb_context_run (mrb=0x69f010, proc=0x6a61b0,
        self=..., stack_keep=0) at mruby/src/vm.c:1126
    #7  0x00000000004131d8 in mrb_toplevel_run_keep (mrb=0x69f010, proc=0x6a61b0,
        stack_keep=0) at mruby/src/vm.c:2422
    #8  0x000000000043a46c in load_exec (mrb=0x69f010, p=0x6f6450, c=0x6c9320)
        at mruby/mrbgems/mruby-compiler/core/parse.y:5619
    #9  0x000000000043a4e2 in mrb_load_file_cxt (mrb=0x69f010, f=0x6f61f0,
        c=0x6c9320)
        at mruby/mrbgems/mruby-compiler/core/parse.y:5628
    #10 0x0000000000402466 in main (argc=2, argv=0x7fffffffe438)
        at mruby/mrbgems/mruby-bin-mruby/tools/mruby/mruby.c:222

add mruby-socket dependency gems

avoid declaration error on VC++

### Example

##### example.rb

```ruby
h = {}
(1..17).each{h[_1] = _1}
(1..16).each{h.delete(_1)}
h.rehash
```

##### ASAN report

```console
$ bin/mruby example.rb
==52587==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000006998 at pc 0x55a29cddf96b bp 0x7fff7b1b1720 sp 0x7fff7b1b1710
READ of size 4 at 0x602000006998 thread T0
    #0 0x55a29cddf96a in ib_it_next /mruby/src/hash.c:639
    mruby#1 0x55a29cde2ca2 in ht_rehash /mruby/src/hash.c:900
    mruby#2 0x55a29cde379f in h_rehash /mruby/src/hash.c:996
    mruby#3 0x55a29cde7f3d in mrb_hash_rehash /mruby/src/hash.c:1735
    mruby#4 0x55a29ce77b62 in mrb_vm_exec /mruby/src/vm.c:1451
    mruby#5 0x55a29ce5fa88 in mrb_vm_run /mruby/src/vm.c:981
    mruby#6 0x55a29ceb87e1 in mrb_top_run /mruby/src/vm.c:2874
    mruby#7 0x55a29cf36bdf in mrb_load_exec mrbgems/mruby-compiler/core/parse.y:6805
    mruby#8 0x55a29cf36f25 in mrb_load_detect_file_cxt mrbgems/mruby-compiler/core/parse.y:6848
    mruby#9 0x55a29cdba0a2 in main /mruby/mrbgems/mruby-bin-mruby/tools/mruby/mruby.c:347
    mruby#10 0x7f24ef43b0b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
    mruby#11 0x55a29cdb4a6d in _start (/mruby/bin/mruby+0x2a3a6d)

0x602000006998 is located 0 bytes to the right of 8-byte region [0x602000006990,0x602000006998)
allocated by thread T0 here:
    #0 0x7f24f01cfffe in __interceptor_realloc (/lib/x86_64-linux-gnu/libasan.so.5+0x10dffe)
    mruby#1 0x55a29ceb9440 in mrb_default_allocf /mruby/src/state.c:68
    mruby#2 0x55a29cdba747 in mrb_realloc_simple /mruby/src/gc.c:228
    mruby#3 0x55a29cdba928 in mrb_realloc /mruby/src/gc.c:242
    mruby#4 0x55a29cde12e5 in ht_init /mruby/src/hash.c:749
    mruby#5 0x55a29cde2b8e in ht_rehash /mruby/src/hash.c:897
    mruby#6 0x55a29cde379f in h_rehash /mruby/src/hash.c:996
    mruby#7 0x55a29cde7f3d in mrb_hash_rehash /mruby/src/hash.c:1735
    mruby#8 0x55a29ce77b62 in mrb_vm_exec /mruby/src/vm.c:1451
    mruby#9 0x55a29ce5fa88 in mrb_vm_run /mruby/src/vm.c:981
    mruby#10 0x55a29ceb87e1 in mrb_top_run /mruby/src/vm.c:2874
    mruby#11 0x55a29cf36bdf in mrb_load_exec mrbgems/mruby-compiler/core/parse.y:6805
    mruby#12 0x55a29cf36f25 in mrb_load_detect_file_cxt mrbgems/mruby-compiler/core/parse.y:6848
    mruby#13 0x55a29cdba0a2 in main /mruby/mrbgems/mruby-bin-mruby/tools/mruby/mruby.c:347
    mruby#14 0x7f24ef43b0b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
```

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