Improve cache file generation

modules/node/init.zsh

@@ -5,15 +5,18 @@
 #   Sorin Ionescu <sorin.ionescu@gmail.com>
 #
 
+if (( ! $+commands[npm] )); then
+  return 1
+fi
+
 cache_file="${0:h}/cache.zsh"
-if [[ ! -s "$cache_file" ]]; then
+
-  if (( $+commands[npm] )); then
+if [[ "$commands[npm]" -nt "$cache_file" || ! -s "$cache_file" ]]; then
   # npm is slow; cache its output.
   npm completion >! "$cache_file" 2> /dev/null
-    source "$cache_file"
 fi
-else
+
 source "$cache_file"
-fi
+
 unset cache_file