attempt to support go module (#1569)

* support go module

* update golint package url

* update golint

tools.go

@@ -0,0 +1,25 @@
+// Copyright 2018 Gin Core Team.  All rights reserved.
+// Use of this source code is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+// +build tools
+
+// This file exists to cause `go mod` and `go get` to believe these tools
+// are dependencies, even though they are not runtime dependencies of any
+// gin package. This means they will appear in `go.mod` file, but will not
+// be a part of the build.
+
+package gin
+
+import (
+	_ "github.com/campoy/embedmd"
+	_ "github.com/client9/misspell/cmd/misspell"
+	_ "github.com/dustin/go-broadcast"
+	_ "github.com/gin-gonic/autotls"
+	_ "github.com/jessevdk/go-assets"
+	_ "github.com/manucorporat/stats"
+	_ "github.com/thinkerou/favicon"
+	_ "golang.org/x/crypto/acme/autocert"
+	_ "golang.org/x/lint/golint"
+	_ "google.golang.org/grpc"
+)