See if we can speed the travis builds with caching

And slightly with pip installing buildout (rather than bootstrapping).

.travis.yml

 language: python
 sudo: false
+cache:
+  pip
+  directories:
+    - eggs
 matrix:
     include:
         - os: linux
@@ -24,9 +28,8 @@ matrix:
           python: 3.5
           env: ZEO4_SERVER=1
 install:
-    - pip install -U setuptools
-    - python bootstrap.py
-    - bin/buildout
+    - pip install -U zc.buildout
+    - buildout
 script:
     - bin/test -v1j99
 notifications: