Do not define $GEM_HOME

Defining it breaks gems for all users who neither use RVM nor rbenv,
but have a different default Ruby version nonetheless.

Signed-off-by: Sorin Ionescu <sorin.ionescu@gmail.com>

modules/ruby/init.zsh

@@ -23,14 +23,9 @@ elif [[ -s "$HOME/.rbenv/bin/rbenv" ]]; then
 elif (( $+commands[rbenv] )); then
   eval "$(rbenv init - --no-rehash zsh)"
 
-# Install local gems according to operating system conventions.
+# Prepend local gems bin directories to PATH.
 else
-  if [[ "$OSTYPE" == darwin* ]]; then
-    export GEM_HOME="$HOME/Library/Ruby/Gems/1.8"
-    path=("$GEM_HOME/bin" $path)
-  else
   path=($HOME/.gem/ruby/*/bin(N) $path)
-  fi
 fi
 
 # Return if requirements are not found.