CI: switch to GitHub Actions - step 1: code style sniffing

This commit:
* Adds a GH Actions workflow for the code style CI check which was previously run on Travis.
* Removes that part of the `.travis.yml` configuration.
* Updates the `.gitattributes` file.
* Adds a separate badge for the CS workflow to the README.

Author: jrfnl

.gitattributes

@@ -1,3 +1,4 @@
+/.github export-ignore
 /tests export-ignore
 .gitattributes export-ignore
 .gitignore export-ignore

.github/workflows/cs.yml

@@ -0,0 +1,35 @@
+name: CS
+
+on:
+  push:
+  pull_request:
+  # Allow manually triggering the workflow.
+  workflow_dispatch:
+
+jobs:
+  checkcs:
+    name: 'Check code style'
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Install PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '7.4'
+          coverage: none
+          tools: cs2pr
+
+      # Install dependencies and handle caching in one go.
+      # @link https://github.com/marketplace/actions/install-composer-dependencies
+      - name: Install Composer dependencies
+        uses: "ramsey/composer-install@v1"
+
+      - name: Check PHP code style
+        continue-on-error: true
+        run: vendor/bin/phpcs --report-full --report-checkstyle=./checkstyle.xml
+
+      - name: Show PHPCS results in PR
+        run: cs2pr ./checkstyle.xml --graceful-warnings

.travis.yml

@@ -44,5 +44,4 @@ before_script:
 
 script:
   - ant phplint
-  - if [[ ${TRAVIS_PHP_VERSION:0:3} == "7.4" ]]; then ant phpcs;fi
   - ant phpunit

README.md

@@ -2,6 +2,7 @@ PHP Console Color
 =================
 
 [![Downloads this Month](https://img.shields.io/packagist/dm/php-parallel-lint/php-console-color.svg)](https://packagist.org/packages/php-parallel-lint/php-console-color)
+[![CS](https://github.com/php-parallel-lint/PHP-Console-Color/actions/workflows/cs.yml/badge.svg)](https://github.com/php-parallel-lint/PHP-Console-Color/actions/workflows/cs.yml)
 [![Build Status](https://travis-ci.org/php-parallel-lint/PHP-Console-Color.svg?branch=master)](https://travis-ci.org/php-parallel-lint/PHP-Console-Color)
 [![License](https://poser.pugx.org/php-parallel-lint/php-console-color/license.svg)](https://packagist.org/packages/php-parallel-lint/php-console-color)