add tools.go

tools.go

@@ -0,0 +1,10 @@
+// +build tools
+
+package main
+
+import (
+	_ "github.com/haya14busa/goverage"
+	_ "github.com/restic/calens"
+	_ "golang.org/x/lint/golint"
+	_ "honnef.co/go/tools/cmd/staticcheck"
+)