Drop docker from binary name for gcr, ecr and heroku

cmd/drone-heroku/main.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+	"os"
+	"os/exec"
+	"path"
+)
+
+func main() {
+	var (
+		registry = "registry.heroku.com"
+		process  = getenv("PLUGIN_PROCESS_TYPE")
+		app      = getenv("PLUGIN_APP")
+		email    = getenv("PLUGIN_EMAIL", "HEROKU_EMAIL")
+		key      = getenv("PLUGIN_API_KEY", "HEROKU_API_KEY")
+	)
+
+	if process == "" {
+		process = "web"
+	}
+
+	os.Setenv("PLUGIN_REGISTRY", registry)
+	os.Setenv("PLUGIN_REPO", path.Join(registry, app, process))
+
+	os.Setenv("DOCKER_PASSWORD", key)
+	os.Setenv("DOCKER_USERNAME", email)
+	os.Setenv("DOCKER_EMAIL", email)
+
+	cmd := exec.Command("drone-docker")
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	err := cmd.Run()
+	if err != nil {
+		os.Exit(1)
+	}
+}
+
+func getenv(key ...string) (s string) {
+	for _, k := range key {
+		s = os.Getenv(k)
+		if s != "" {
+			return
+		}
+	}
+	return
+}