Use c instead of python as language

Otherwise it installs a different version of python. We want to test the
exact dependencies whenever possible.

.travis.yml

@@ -1,8 +1,6 @@
-language: python
+language: c
 
 before_install:
-  - sudo apt-get -y install make
-
   - sudo apt-get -y install python-pip
 
   - sudo apt-get -y install python-software-properties