remove matrix

.travis.yml

 language: python
-matrix:
-  include:
-    - python: "2.7"
-    - python: "3.6"
-    # works on Precise and Trusty
-    - os: linux
+python:
+  - "2.7"
+  - "3.6"
+os:
+  - linux
     addons:
       apt:
         sources:
@@ -14,9 +13,7 @@ matrix:
     env:
        - CC=gcc-4.9
        - CXX=g++-4.9"
-
-    # works on Precise and Trusty
-    - os: linux
+  - linux
     addons:
       apt:
         sources: