Notify slack for travis builds

.travis.yml

@@ -12,6 +12,7 @@ script: ./travis-compile.sh
 install: ./travis-dependencies.sh
 cache: apt
 notifications:
+  slack: cockatrice:dNA81maCU8SAHB7pYrCWiQg9
   webhooks:
     urls:
       - https://webhooks.gitter.im/e/d94969c3b01b22cbdcb7
@@ -19,4 +20,4 @@ notifications:
     on_failure: change
     on_start: false
 matrix:
-  fast_finish: true
\ No newline at end of file
+  fast_finish: true