add travis file based of of this article

https://medium.com/flutter-io/why-you-should-smoke-test-your-sample-code-and-how-to-do-it-in-flutter-ddaba88ce71e

Author: taljacobson

.travis.yml

@@ -0,0 +1,26 @@
+os:
+  - linux
+sudo: false
+addons:
+  apt:
+    sources:
+      - ubuntu-toolchain-r-test
+    packages:
+      - libstdc++6
+      - fonts-droid
+git:
+  depth: 3
+cache:
+  directories:
+    - $HOME/.pub-cache
+env:
+  - FLUTTER_VERSION=beta
+  - FLUTTER_VERSION=dev
+matrix:
+  allow_failures:
+    - env: FLUTTER_VERSION=dev
+before_script:
+  - git clone https://github.com/flutter/flutter.git -b $FLUTTER_VERSION
+  - ./flutter/bin/flutter doctor
+script:
+  - ./flutter/bin/flutter test example/test/widget_test.dart

example/test/widget_test.dart

@@ -7,7 +7,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-import 'package:example/main.dart';
+import '../lib/main.dart';
 
 void main() {
   testWidgets('Skip Pressed smoke test', (WidgetTester tester) async {