Fix linux-bazel build (#566)

Install bazel via apt-source
diff --git a/.travis.yml b/.travis.yml
index fe05e44..73a7615 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -235,10 +235,12 @@
       addons:
         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"
             - ubuntu-toolchain-r-test
           packages:
-            - wget
-            - pkg-config
+            - oracle-java8-installer
+            - bazel
 
     - os: osx
       env: BUILD_SYSTEM=bazel