feat(cli): version flag (#60)

* feat(cli): version flag

Adds a --version flag to jb. Only available on go versions greater than 1.12

* style: add license headers

* chore(ci): generate only on latest go

* fix: unique step names

* doc: include version in README help text

* fix: rebuild .drone.yml using drone.cli

* fix: remove race condidion from CI

cmd/jb/version.go

@@ -0,0 +1,34 @@
+// Copyright 2018 jsonnet-bundler authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build go1.12
+
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"runtime/debug"
+
+	kingpin "gopkg.in/alecthomas/kingpin.v2"
+)
+
+func newApp() *kingpin.Application {
+	a := kingpin.New(filepath.Base(os.Args[0]), "A jsonnet package manager")
+	d, ok := debug.ReadBuildInfo()
+	if ok {
+		return a.Version(d.Main.Version)
+	}
+	return a
+}