Added caching to Travis config and cleaned it up.

Author: kgodey

.travis.yml

@@ -1,11 +1,13 @@
 language: python
-python:
-  - "3.7-dev"  # 3.7 development branch
+python: "3.7-dev"  # 3.7 development branch
+cache:
+  directories:
+    - $HOME/.cache/pip
+    - $HOME/.cache/lektor/builds
 install:
   - pip install pipenv
   - pipenv install
-script:
-  - lektor build
+script: lektor build
 deploy:
   provider: script
-  script: lektor deploy
+  script: lektor deploy ghpages