Fix broken windows install script - #97

PS C:\Users\Richard Wall> irm https://raw.githubusercontent.com/jetstack/jsctl/fix_windows_install/install.ps1 | iex
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jsctl was installed successfully to C:\Users\Richard Wall\.jsctl\bin\jsctl.exe
Run 'jsctl --help' to get started
Checkout https://platform.jetstack.io/documentation for more information
PS C:\Users\Richard Wall> jsctl.exe
Command-line tool for the Jetstack Secure Control Plane

Usage:
  jsctl [command]

Available Commands:
  auth          Subcommands for authentication
  clusters      Subcommands for cluster management
  completion    Generate the autocompletion script for the specified shell
  configuration Subcommands for configuration management
  experimental  Experimental jsctl commands
  help          Help about any command
  operator      Subcommands for managing the Jetstack operator
  organizations Subcommands for organization management
  registry      Subcommands for Jetstack Secure registry management
  users         Subcommands for user management
  version       view the version, commit and build date of jsctl

Flags:
      --api-url string      Base URL of the control-plane API (default "https://platform.jetstack.io")
      --config string       Location of the user's jsctl config directory (default "C:\\Users\\Richard Wall\\.jsctl")
  -h, --help                help for jsctl
      --kubeconfig string   Location of the user's kubeconfig file for applying directly to the cluster (default "~/.kube/config")
      --stdout              If provided, manifests are written to stdout rather than applied to the current cluster
  -v, --version             version for jsctl

Use "jsctl [command] --help" for more information about a command.