[Travis] Release the jar when we apply a tag.

The plugin's jar file can be stored in github releases
(https://github.com/criteo/automerge-plugin/releases) after a
travis build. Let's do that each time we apply a tag to the
github account.

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index 6da06d4..2f70730 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -34,3 +34,12 @@
 script:
   - ../buck/bin/buck build gerrit > buck.log
   - ../buck/bin/buck build plugins/automerge-plugin:automerge-plugin >> buck.log
+
+deploy:
+  provider: releases
+  api_key:
+    secure: Hze64QC7F5SSOVoufSIPtRWb+t6Pzzvx2kJgLtPJYUj87CKOXYzVHVqHuWsa50DPfed9knDnm5nOJawZAxleXG5VxSvBERvSyUNhjNUbDkKson1/TcCl12YM5FcyM2ocsLYe/mc59V3h9LZR2mHDqVj/incxwAIxV/MJIgu5PBg=
+  file: buck-out/gen/plugins/automerge-plugin/automerge-plugin.jar
+  on:
+    repo: criteo/automerge-plugin
+    tags: true