Travis: explicitly install python3.4-dev

Author: Clement Champetier

.travis.yml

@@ -75,7 +75,7 @@ after_failure:
 
 addons:
   apt:
-    sources: ['boost-latest', 'kalakris-cmake', 'kubuntu-backports', 'pythonxy-devel']
+    sources: ['boost-latest', 'kalakris-cmake', 'kubuntu-backports', 'pythonxy-devel', 'deadsnakes']
     packages:
     - cmake
     - swig
@@ -84,7 +84,7 @@ addons:
     - python-imaging
     - python-numpy
     - python-nose
-    - python3-dev
+    - python3.4-dev
     - python3-setuptools
     - python3-nose
     - libfreetype6-dev