Update Travis config with new URL for bazel signing key (#53)

diff --git a/.travis.yml b/.travis.yml
index e35dd5d..e1687c5 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -8,7 +8,7 @@
   apt:
     sources:
       - sourceline: 'deb [arch=amd64] http://storage.googleapis.com/bazel-apt stable jdk1.8'
-        key_url: 'https://storage.googleapis.com/bazel-apt/doc/apt-key.pub.gpg'
+        key_url: 'https://bazel.build/bazel-release.pub.gpg'
     packages:
       - bazel
 script: