Merge pull request #3409 from unixorn/prevent-variable-clobbering

Add quoting to nvm.sh

lib/nvm.zsh

 # get the node.js version
 function nvm_prompt_info() {
-  [ -f $HOME/.nvm/nvm.sh ] || return
+  [ -f "$HOME/.nvm/nvm.sh" ] || return
   local nvm_prompt
   nvm_prompt=$(node -v 2>/dev/null)
   [[ "${nvm_prompt}x" == "x" ]] && return