Add go.mod manifest

This file specifies the require path for go-mail and the v2 branch.

Fixes #39

Author: ivy

CHANGELOG.md

@@ -10,6 +10,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   a failed attempt to transmit a batch of messages.
 - go-gomail#78: Adds new `Message` methods for attaching and embedding
   `io.Reader`s: `AttachReader` and `EmbedReader`.
+- #39: Adds support for Go modules (Go 1.11+).
 
 ### Fixed
 

go.mod

@@ -0,0 +1 @@
+module github.com/go-mail/mail/v2