Update toolchain

* Use go modules
 * Remove vendor/

go.mod

@@ -0,0 +1,23 @@
+module github.com/yudai/gotty
+
+go 1.11
+
+require (
+	github.com/NYTimes/gziphandler v1.1.1
+	github.com/elazarl/go-bindata-assetfs v1.0.1
+	github.com/fatih/structs v1.1.0
+	github.com/gorilla/websocket v1.4.2
+	github.com/hashicorp/go-multierror v1.1.1 // indirect
+	github.com/jteeuwen/go-bindata v3.0.7+incompatible // indirect
+	github.com/kr/fs v0.1.0 // indirect
+	github.com/kr/pretty v0.2.1 // indirect
+	github.com/kr/pty v1.1.8
+	github.com/mitchellh/gox v1.0.1 // indirect
+	github.com/pkg/errors v0.9.1
+	github.com/tcnksm/ghr v0.13.0 // indirect
+	github.com/tools/godep v0.0.0-20180126220526-ce0bfadeb516 // indirect
+	github.com/urfave/cli v1.22.5
+	github.com/yudai/hcl v0.0.0-20151013225006-5fa2393b3552
+	golang.org/x/sys v0.0.0-20210403161142-5e06dd20ab57 // indirect
+	golang.org/x/tools v0.1.0 // indirect
+)