Improve regex pattern to match only modifiers

Modifiers need to be proceeded by a non-slash ("/") character.

    foo/(osx|darwin)

is not valid.

base/utils/shell.zsh

@@ -184,7 +184,7 @@ __zplug::utils::shell::expand_glob()
     local -a matches
 
     # Modifiers not specified (by user)
-    if [[ ! $pattern =~ '\([^)]*\)$' ]]; then
+    if [[ ! $pattern =~ '[^/]\([^)]*\)$' ]]; then
         pattern+="$default_modifiers"
     fi