fix 'needs_to_reload?' regexps

- remove stray ^ that would cause regexp to never match
- remove '_helper' suffix as it isn't required for helpers

middleman-core/lib/middleman-core/preview_server.rb

@@ -189,8 +189,8 @@ module Middleman
       def needs_to_reload?(paths)
         match_against = [
           %r{^config\.rb},
-          %r{^lib/^[^\.](.*)\.rb$},
-          %r{^helpers/^[^\.](.*)_helper\.rb$}
+          %r{^lib/[^\.](.*)\.rb$},
+          %r{^helpers/[^\.](.*)\.rb$}
         ]
 
         if @options[:reload_paths]