move $GOPATH/bin to end of $PATH

Closes go-nv#99.

INSTALL.md

@@ -39,7 +39,7 @@ easy to fork and contribute any changes back upstream.
   add `GOPATH` and `GOROOT` to your shell **after `eval "$(goenv init -)"`**.
 
         $ echo 'export PATH="$GOROOT/bin:$PATH"' >> ~/.bash_profile
-        $ echo 'export PATH="$GOPATH/bin:$PATH"' >> ~/.bash_profile
+        $ echo 'export PATH="$PATH:$GOPATH/bin"' >> ~/.bash_profile
         
     **Zsh note**: Modify your `~/.zshenv` or `~/.zshrc` file instead of `~/.bash_profile`.
     **Ubuntu note**: Modify your `~/.bashrc` file instead of `~/.bash_profile`.
@@ -48,6 +48,11 @@ easy to fork and contribute any changes back upstream.
     `eval "$(goenv init -)` into `.bash_profile`, and **not** into `.bashrc`. Otherwise you
     may observe strange behaviour, such as `goenv` getting into an infinite loop.
     See pyenv's issue [#264](https://github.com/yyuu/pyenv/issues/264) for details.
+
+    **Security warning**: You likely want to keep $GOPATH/bin at the end
+    of your $PATH as shown above, rather than at the beginning.  See
+    [#99](https://github.com/syndbg/goenv/issues/99) for details and
+    discussion.
 
 
 5. **Restart your shell so the path changes take effect.**
@@ -69,7 +74,7 @@ export GOENV_ROOT="$HOME/.goenv"
 export PATH="$GOENV_ROOT/bin:$PATH"
 eval "$(goenv init -)"
 export PATH="$GOROOT/bin:$PATH"
-export PATH="$GOPATH/bin:$PATH"
+export PATH="$PATH:$GOPATH/bin"
 ```
 
 ## Homebrew on Mac OS X