Attempt fixing the travis configuration

.travis.yml

@@ -1,31 +1,31 @@
 language: dart
 dart:
-  - stable
+  - dev
 
 jobs:
   include:
     - stage: valid
       name: "Dart Analyzer"
       os: linux
-      script: dart --enable-experiment=non-nullable analyze --fatal-warnings --fatal-infos .
+      script: dartanalyzer --fatal-infos .
     - stage: valid
       name: "Dart Formatter"
       os: linux
-      script: dart --enable-experiment=non-nullable format --output=none .
+      script: dartfmt --dry-run --set-exit-if-changed .
     - stage: test
       name: "VM Tests"
       os: linux
-      script: dart --enable-experiment=non-nullable test --platform vm test/all_test.dart
+      script: pub run test test/all_test.dart --platform vm
     - stage: test
       name: "Chrome Tests"
       os: linux
-      script: dart --enable-experiment=non-nullable test --platform chrome test/all_test.dart
+      script: pub run test test/all_test.dart --platform chrome
+    - stage: coverage
+      name: "Coverage"
+      os: linux
+      script: pub global activate dart_coveralls && dart_coveralls report test/all_test.dart
 
 stages:
   - valid
   - test
-
-after_success:
-  - pub global activate dart_coveralls
-  - pub global run --enable-experiment=non-nullable dart_coveralls report test/all_test.dart
-
+  - coverage