Use the lazy-loaded version of virtualenvwrapper if available

This shouldn't cause problems for anyone and should improve startup times for
anyone using python with virtualenvwrapper because it will wait for the first
command to load rather than right away.

modules/python/init.zsh

@@ -46,6 +46,8 @@ if zstyle -T ':prezto:module:python' skip-virtualenvwrapper-init; then
     pyenv virtualenvwrapper
   elif (( $+commands[pyenv-virtualenv-init] )); then
     eval "$(pyenv virtualenv-init -)"
+  elif (( $+commands[virtualenvwrapper_lazy.sh] )); then
+    source "$commands[virtualenvwrapper_lazy.sh]"
   elif (( $+commands[virtualenvwrapper.sh] )); then
     source "$commands[virtualenvwrapper.sh]"
   fi