Use Github actions instead of travis

+name: Dart CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - uses: subosito/flutter-action@v1
+    - name: Install utils
+      run: sudo apt install poppler-utils imagemagick
+    - name: Run analysis
+      run: make analyze
+    - name: Run tests
+      run: make test
+    - name: Run readme tests
+      run: make test-readme
+    - name: Verify that nothing changed
+      run: test -z "$(git status --porcelain)"
+    - name: Push to codecov
+      run: bash <(curl -s https://codecov.io/bash)

-language: dart
-dist: bionic
-addons:
-  apt:
-    packages:
-      - lib32stdc++6
-      - poppler-utils
-      - imagemagick
-install:
-  - git clone https://github.com/flutter/flutter.git -b stable --depth 1 $HOME/flutter
-  - export PATH=$HOME/flutter/bin:$PATH
-  - flutter doctor
-  - flutter --version
-script:
-  - make analyze
-  - make test
-  - make test-readme
-  - bash <(curl -s https://codecov.io/bash)
-cache:
-  directories:
-    - $HOME/.pub-cache

 # Pdf for Dart and Flutter
 
-[![Build Status](https://travis-ci.org/DavBfr/dart_pdf.svg?branch=master)](https://travis-ci.org/DavBfr/dart_pdf)
+![Dart CI](https://github.com/DavBfr/dart_pdf/workflows/Dart%20CI/badge.svg)
 [![pub package](https://img.shields.io/pub/v/pdf.svg)](https://pub.dartlang.org/packages/pdf)
 [![pub package](https://img.shields.io/pub/v/printing.svg)](https://pub.dartlang.org/packages/printing)
 [![codecov](https://codecov.io/gh/DavBfr/dart_pdf/branch/master/graph/badge.svg)](https://codecov.io/gh/DavBfr/dart_pdf)