docs: update README w.r.t new maintainer ask (#660)

* Update README.md

* build: gofmt on latest

Author: elithrar

Diff for: README.md

@@ -6,7 +6,11 @@
 
 ![Gorilla Logo](https://cloud-cdn.questionable.services/gorilla-icon-64.png)
 
-https://www.gorillatoolkit.org/pkg/mux
+---
+
+⚠️ **[The Gorilla Toolkit is looking for a new maintainer](https://github.com/gorilla/mux/issues/659)**
+
+---
 
 Package `gorilla/mux` implements a request router and dispatcher for matching incoming requests to
 their respective handler.

Diff for: mux_httpserver_test.go

@@ -1,3 +1,4 @@
+//go:build go1.9
 // +build go1.9
 
 package mux