fix(chruby): update brew sourcing for Apple Silicon

plugins/chruby/chruby.plugin.zsh

@@ -16,14 +16,15 @@ _source-from-omz-settings() {
 }
 
 _source-from-homebrew() {
-  (( $+commands[brew] )) || return 1
-
   local _brew_prefix
   # check default brew prefix
-  if [[ -h /usr/local/opt/chruby ]];then
-    _brew_prefix="/usr/local/opt/chruby"
+  if [[ -h /opt/homebrew/opt/chruby ]]; then
+    _brew_prefix="/opt/homebrew/opt/chruby"
   else
     # ok , it is not default prefix
+    # check to see if brew command is available
+    (( $+commands[brew] )) || return 1
+
     # this call to brew is expensive ( about 400 ms ), so at least let's make it only once
     _brew_prefix=$(brew --prefix chruby)
   fi