Fix spec path verification with multiple pattern

RSpec.configuration.pattern may not satisfy a glob pattern
if multiple pattern is set (e.g. '**{,/*/**}/*_spec.rb,**/*.feature').

See also RSpec::Core::Configuration#file_glob_from.

lib/guard/rspec_formatter.rb

@@ -77,7 +77,8 @@ def self.spec_path?(path)
       path ||= ""
       path = path.sub(/:\d+\z/, "")
       path = Pathname.new(path).cleanpath.to_s
-      File.fnmatch(pattern, path, flags)
+      stripped = "{#{pattern.gsub(/\s*,\s*/, ',')}}"
+      File.fnmatch(stripped, path, flags)
     end
 
     def dump_summary(*args)