fix: export napi symbols (#77)

nornagon · deepak1556 · commit 1293d1d7d0c3 · 2018-12-25T07:01:26.000+05:30
matches the change in node.h in 88b4941, both are necessary because Chromium builds with symbols hidden by default
diff --git a/src/js_native_api.h b/src/js_native_api.h
@@ -21,7 +21,7 @@
   #ifdef _WIN32
     #define NAPI_EXTERN __declspec(dllexport)
   #else
-    #define NAPI_EXTERN /* nothing */
+    #define NAPI_EXTERN __attribute__((visibility("default")))
   #endif
 #endif
 
