Fix the outdated _npm completion script

[Hong Xu <hong@xxxxxxxxxx>]

Hi,

The existing npm completion script no longer works. The stdout of `npm 
completion` has become a script to add a completion function. Here is 
the patch to update it.

Hong

diff --git a/Completion/Unix/Command/_npm b/Completion/Unix/Command/_npm
index 24b5361..d9d6287 100644
--- a/Completion/Unix/Command/_npm
+++ b/Completion/Unix/Command/_npm
@@ -1,19 +1,7 @@
 #compdef npm
 
-# Node Package Manager 0.3.15 completion, letting npm do all the completion work
+# Node Package Manager completion, letting npm do all the completion work
 
-_npm() {
-  compadd -- $(_npm_complete $words)
-}
+eval "$(npm completion)"
 
-# We want to show all errors of any substance, but never the "npm (not )ok" one.
-# (Also doesn't consider "ERR! no match found" worth breaking the terminal for.)
-_npm_complete() {
-  local ask_npm
-  ask_npm=(npm completion --color false --loglevel error -- $@)
-  { _call_program npm $ask_npm 2>&1 >&3 \
-  | egrep -v '^(npm (not |)ok|ERR! no match found)$' >&2; \
-  } 3>&1
-}
-
-_npm "$@"
+_npm_completion "$@"