Migrate to GitHub actions for CI testing

Travis CI no longer seems to be working:
https://app.travis-ci.com/github/mattn/go-colorable

Add a GitHub action instead, based on the one from
github.com/mattn/go-isatty

.github/workflows/test.yml

@@ -0,0 +1,41 @@
+name: test
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  test:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+          - ubuntu-latest
+          - macos-latest
+          - windows-latest
+        go:
+          - '1.17'
+          - '1.16'
+          - '1.15'
+          - '1.14'
+          - '1.13'
+    steps:
+      - uses: actions/setup-go@v2
+        with:
+          go-versions: ${{ matrix.go }}
+      - uses: actions/checkout@v2
+      - name: test
+        shell: bash
+        run: |
+          ./go.test.sh
+      - name: upload coverage report
+        uses: codecov/codecov-action@v2
+        with:
+          env_vars: OS,GO
+        env:
+          OS: ${{ matrix.os }}
+          GO: ${{ matrix.go }}

README.md

@@ -1,6 +1,6 @@
 # go-colorable
 
-[![Build Status](https://travis-ci.org/mattn/go-colorable.svg?branch=master)](https://travis-ci.org/mattn/go-colorable)
+[![Build Status](https://github.com/mattn/go-colorable/workflows/test/badge.svg)](https://github.com/mattn/go-colorable/actions?query=workflow%3Atest)
 [![Codecov](https://codecov.io/gh/mattn/go-colorable/branch/master/graph/badge.svg)](https://codecov.io/gh/mattn/go-colorable)
 [![GoDoc](https://godoc.org/github.com/mattn/go-colorable?status.svg)](http://godoc.org/github.com/mattn/go-colorable)
 [![Go Report Card](https://goreportcard.com/badge/mattn/go-colorable)](https://goreportcard.com/report/mattn/go-colorable)