Add zeromq.

Install bower dependencies.
Cache dependencies.

.travis.yml

@@ -3,3 +3,12 @@ node_js:
   - "0.12"
   - "0.10"
   - "iojs"
+before_install:
+  - sudo apt-get install -qq libzmq3-dev libsodium-dev
+before_script:
+  - ./node_modules/bower/bin/bower install
+cache:
+  apt
+  directories:
+    - node_modules
+    - res/bower_components