travis: use build stages and publish release automatically

.travis.yml

@@ -1,11 +1,9 @@
 language: go
-go_import_path: github.com/getamis/istanbul-tools
 sudo: required
-os: linux
-dist: trusty
 go:
-  - 1.7.6
-  - 1.8.3
+  - 1.7
+  - 1.8
+  - 1.9
 env:
   - TEST=unit
   - TEST=istanbul
@@ -29,6 +27,24 @@ script:
       echo "Invalid env"
       exit 2;
     fi'
+branches:
+  only:
+    - develop
+
+jobs:
+  include:
+    - stage: release
+      go: 1.9
+      if: tag =~ ^v
+      env:
+        - TEST=none
+        - REV="$TRAVIS_TAG"
+      deploy:
+        provider: releases
+        api_key: "$GITHUB_OAUTH_TOKEN"
+        skip_cleanup: true
+        on:
+          tags: true
 
 notifications:
   webhooks: