Update travis-ci to test on latest dev (#38)

diff --git a/.travis.yml b/.travis.yml
index ca6ce1b..f87ab52 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,33 +1,28 @@
 language: dart
 dart:
-  - preview/raw/2.10.0-0.2-dev
+  - dev
 
 jobs:
   include:
     - stage: analyze_and_format
       name: "Analyze lib/"
-      dart: preview/raw/2.10.0-0.2-dev
       os: linux
       script: dartanalyzer --fatal-warnings --fatal-infos lib/
     # Dirs outside of `lib` are not supported by allowed_experiments.json
     - stage: analyze_and_format
       name: "Analyze test/"
-      dart: preview/raw/2.10.0-0.2-dev
       os: linux
       script: dartanalyzer --enable-experiment=non-nullable --fatal-warnings --fatal-infos test/
     - stage: analyze_and_format
       name: "Format"
-      dart: preview/raw/2.10.0-0.2-dev
       os: linux
       script: dartfmt -n --set-exit-if-changed .
     - stage: test
       name: "Vm Tests"
-      dart: preview/raw/2.10.0-0.2-dev
       os: linux
       script: pub run --enable-experiment=non-nullable test -p vm 
     - stage: test
       name: "Web Tests"
-      dart: preview/raw/2.10.0-0.2-dev
       os: linux
       script: pub run --enable-experiment=non-nullable test -p chrome