Fix travis build

Author: simc

.gitattributes

@@ -1,20 +1,23 @@
 os:
-  - linux
+  - osx
+env:
+  - FLUTTER_CHANNEL="stable"
+  - FLUTTER_CHANNEL="master"
 sudo: false
-addons:
-  apt:
-    # Flutter depends on /usr/lib/x86_64-linux-gnu/libstdc++.so.6 version GLIBCXX_3.4.18
-    sources:
-      - ubuntu-toolchain-r-test # if we don't specify this, the libstdc++6 we get is the wrong version
-    packages:
-      - libstdc++6
-      - fonts-droid
 before_script:
-  - git clone https://github.com/flutter/flutter.git -b beta
-  - ./flutter/bin/flutter doctor
+  - cd ..
+  - git clone https://github.com/flutter/flutter.git -b $FLUTTER_CHANNEL
+  - export PATH=$PATH:$PWD/flutter/bin:$PWD/flutter/bin/cache/dart-sdk/bin
+  - cd -
+  - flutter doctor
 script:
-  - ./flutter/bin/flutter pub get
-  - ./flutter/bin/cache/dart-sdk/bin/dartfmt -n --set-exit-if-changed ./lib ./test ./example || travis_terminate 1
+  - set -e # abort CI if an error happens
+  - flutter pub get
+  - dartfmt -n --set-exit-if-changed ./lib ./test ./example || travis_terminate 1
+matrix:
+  fast_finish: true
+  allow_failures:
+  - env: FLUTTER_CHANNEL="master"
 cache:
   directories:
     - $HOME/.pub-cache