environment: override GEM_HOME to prevent ~/.gem

Note from the Arch Wiki:
    Make sure to remove gem: --user-install from /etc/gemrc

https://wiki.archlinux.org/index.php/XDG_Base_Directory#Ruby

Signed-off-by: Joe Groocock <me@frebib.net>

environment.d/20-xdg-overrides.conf

@@ -4,6 +4,8 @@
 ASPELL_CONF="per-conf $XDG_CONFIG_HOME/aspell/aspell.conf; personal $XDG_CONFIG_HOME/aspell/en.pws; repl $XDG_CONFIG_HOME/aspell/en.prepl"
 CARGO_HOME="$XDG_DATA_HOME/cargo"
 GNUPGHOME="$XDG_CONFIG_HOME/gnupg"
+GEM_HOME="$XDG_DATA_HOME/gem"
+GEM_SPEC_CACHE="$XDG_CACHE_HOME/gem"
 GOPATH="$XDG_DATA_HOME/go"
 ICEAUTHORITY="$XDG_CACHE_HOME/ICEauthority"
 NPM_CONFIG_USERCONFIG="$XDG_CONFIG_HOME/npm/npmrc"
@@ -20,6 +22,6 @@ WEECHAT_HOME="$XDG_CONFIG_HOME/weechat"
 XINITRC="$XDG_CONFIG_HOME/X11/xinitrc"
 ZDOTDIR="$XDG_CONFIG_HOME/zsh"
 
-PATH="${PATH}:${GOPATH}/bin"
+PATH="${PATH}:${GOPATH}/bin:${GEM_HOME}/bin"
 
 # vim: ft=sh