Update Travis-CI config

Author: jim-easterbrook

.travis.yml

@@ -1,14 +1,17 @@
 language: python
 python:
   - "2.7"
-  - "3.5"
+  - "3.6"
 
 before_install:
-  - sudo apt-get update -qq
-  - sudo apt-get install -qq swig libgphoto2-2-dev
+  - sudo apt-get install -y swig libgphoto2-dev
 
 script:
   - python setup.py build_swig
+  - PYTHON_GPHOTO2_BUILTIN=1 python setup.py build
+  - rm -rf build
   - PYTHON_GPHOTO2_NO_BUILTIN=1 python setup.py build
   - rm -rf build
+  - PYTHON_GPHOTO2_BUILTIN=1 CC=clang python setup.py build
+  - rm -rf build
   - PYTHON_GPHOTO2_NO_BUILTIN=1 CC=clang python setup.py build