add brew install path to search

recent `brew install jenv` installs to `/usr/local/bin/jenv`, auto-discover it for recent brew installs to avoid secondary, slower search

plugins/jenv/jenv.plugin.zsh

-jenvdirs=("$HOME/.jenv" "/usr/local/jenv" "/opt/jenv")
+jenvdirs=("$HOME/.jenv" "/usr/local" "/usr/local/jenv" "/opt/jenv")
 
 FOUND_JENV=0
 for jenvdir in $jenvdirs; do