Fix error output when grep shell functions

For the error output "grep: (standard input): binary file matches",
we should redirect the error output to /dev/null.

Author: jeffreytse

alias-tips.plugin.zsh

@@ -43,7 +43,7 @@ _alias_tips__preexec () {
   shell_aliases=$(\alias)
 
   local shell_functions
-  shell_functions=$(\functions | \egrep '^[a-zA-Z].+ \(\) \{$')
+  shell_functions=$(\functions | \egrep '^[a-zA-Z].+ \(\) \{$' 2> /dev/null)
 
   # Exit code returned from python script when we want to force use of aliases.
   local force_exit_code=10