Run travis jobs on stable as well as dev (#115)

diff --git a/.travis.yml b/.travis.yml
index e7bbdc3..ad8dd94 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -15,10 +15,18 @@
     env: PROTOC_VERSION=3.3.0
     install: ./tool/travis/setup.sh
     script: ./tool/travis/analyze.sh
+  - dart: stable
+    env: PROTOC_VERSION=3.3.0
+    install: ./tool/travis/setup.sh
+    script: ./tool/travis/analyze.sh
   - dart: dev
     env: PROTOC_VERSION=3.3.0
     install: ./tool/travis/setup.sh
     script: ./tool/travis/test.sh
+  - dart: stable
+    env: PROTOC_VERSION=3.3.0
+    install: ./tool/travis/setup.sh
+    script: ./tool/travis/test.sh
 
 branches:
   only: [master]