bugfixes and updated go.mod

vendor/github.com/gorilla/mux/context_native.go

@@ -1,24 +0,0 @@
-// +build go1.7
-
-package mux
-
-import (
-	"context"
-	"net/http"
-)
-
-func contextGet(r *http.Request, key interface{}) interface{} {
-	return r.Context().Value(key)
-}
-
-func contextSet(r *http.Request, key, val interface{}) *http.Request {
-	if val == nil {
-		return r
-	}
-
-	return r.WithContext(context.WithValue(r.Context(), key, val))
-}
-
-func contextClear(r *http.Request) {
-	return
-}