Migrate from Travis CI to GitHub Actions

This simply rewrites the Travis CI config format to GitHub Actions, while
keeping the same (old) Go versions (but ignoring "tip" since that's too new).

We can incrementally migrate to newer, supported versions of Go after we've
validated that this format works with the current Go versions.

Fixes #85

.github/workflows/go.yaml

@@ -0,0 +1,30 @@
+name: "Go"
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  go:
+    strategy:
+      fail-fast: false
+      matrix:
+        go: [ '1.14', '1.13', '1.12' ]
+        os: [ 'ubuntu-22.04' ]
+    runs-on: ${{ matrix.os }}
+    name: Go ${{ matrix.go }} on ${{ matrix.os }}
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v4
+
+      - name: Setup Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: ${{ matrix.go }}
+
+      - name: Build
+        run: go test ./...
+        env:
+          GO111MODULE: on

README.md

@@ -1,7 +1,7 @@
 # soy
 
 [![GoDoc](http://godoc.org/github.com/robfig/soy?status.png)](http://godoc.org/github.com/robfig/soy)
-[![Build Status](https://travis-ci.org/robfig/soy.png?branch=master)](https://travis-ci.org/robfig/soy)
+[![Build Status](https://github.com/robfig/soy/actions/workflows/go.yaml/badge.svg?query=branch%3Amaster)](https://github.com/robfig/soy/actions/workflows/go.yaml?query=branch%3Amaster)
 [![Go Report Card](https://goreportcard.com/badge/robfig/soy)](https://goreportcard.com/report/robfig/soy)
 
 Go implementation for Soy templates aka [Google Closure