Update travis and use go modules

.travis.yml

@@ -1,25 +1,13 @@
 language: go
 
 go:
-  - 1.2
-  - 1.3
-  - 1.4
-  - 1.5
-  - 1.6
-  - 1.7
-  - 1.8
-  - 1.9
-  - master
+  - "1.13"
+  - tip
 
-# safelist
-branches:
-  only:
-  - master
-  - v2
+go_import_path: github.com/Shopify/gomail
 
-notifications:
-  email: false
+script:
+  - make coverage
 
-before_install:
-  - mkdir -p $GOPATH/src/gopkg.in &&
-    ln -s ../github.com/go-mail/mail $GOPATH/src/gopkg.in/mail.v2
+after_success:
+  - if [[ -f "coverage.txt" ]]; then bash <(curl -s https://codecov.io/bash); fi

Makefile

@@ -0,0 +1,23 @@
+GOFILES := $(shell find . -path ./vendor -prune -o -type f -name '*.go' -print)
+
+all: test
+
+test:
+	go test ./...
+
+coverage: coverage.txt
+
+coverage.txt: $(GOFILES) Makefile
+	go test -coverprofile=coverage.txt -covermode=atomic ./...
+
+show-coverage: coverage.txt
+	go tool cover -html=coverage.txt
+
+style: $(GOFILES) Makefile .golangci.yml
+	bin/style
+
+clean:
+	go clean
+	rm -f coverage.txt
+
+.PHONY: clean test coverage show-coverage

dev.yml

@@ -0,0 +1,14 @@
+name: gomail
+
+up:
+  - go:
+      version: "1.13.7"
+      modules: true
+
+commands:
+  test: go test -race ./...
+  style:
+    run: bin/style
+    desc: Static verification using golangci or autofix issues when possible.
+    syntax:
+      optional: --fix

go.mod

@@ -0,0 +1,8 @@
+module github.com/Shopify/gomail
+
+go 1.13
+
+require (
+	gopkg.in/alexcesaro/quotedprintable.v3 v3.0.0-20150716171945-2caba252f4dc
+	gopkg.in/mail.v2 v2.3.1
+)

go.sum

@@ -0,0 +1,4 @@
+gopkg.in/alexcesaro/quotedprintable.v3 v3.0.0-20150716171945-2caba252f4dc h1:2gGKlE2+asNV9m7xrywl36YYNnBG5ZQ0r/BOOxqPpmk=
+gopkg.in/alexcesaro/quotedprintable.v3 v3.0.0-20150716171945-2caba252f4dc/go.mod h1:m7x9LTH6d71AHyAX77c9yqWCCa3UKHcVEj9y7hAtKDk=
+gopkg.in/mail.v2 v2.3.1 h1:WYFn/oANrAGP2C0dcV6/pbkPzv8yGzqTjPmTeO7qoXk=
+gopkg.in/mail.v2 v2.3.1/go.mod h1:htwXN1Qh09vZJ1NVKxQqHPBaCBbzKhp5GzuJEA4VJWw=