Add support for ruby gem paths and rvm

Update convention to use -s over !-f

zshenv

@@ -1,10 +1,20 @@
 export EDITOR="nvim"
 export GPG_TTY=$(tty)
+export NVM_DIR="$HOME/.nvm"
 
 fpath+=(~/.zsh/completions)
 
 # Setup cargo
-[[ ! -f ~/.cargo/env ]] || source ~/.cargo/env
+[[ -s ~/.cargo/env ]] && source ~/.cargo/env
 
 # Source machine-specific environment
-[[ ! -f ~/.zshenv.local ]] || source ~/.zshenv.local
+[[ -s ~/.zshenv.local ]] && source ~/.zshenv.local
+
+# Local gems
+if (( $+commands[ruby] )); then
+  local gem_bin_path="$(ruby -r rubygems -e 'puts Gem.user_dir')/bin"
+  [[ -d "$gem_bin_path" ]] && path+=("$gem_bin_path")
+fi
+
+# Add RVM to PATH for scripting. Make sure this is the last PATH variable change.
+[[  -d "$HOME/.rvm/bin"  ]] && path+=("$HOME/.rvm/bin")