Simplify

Author: d-frey

.travis.yml

@@ -15,31 +15,27 @@ matrix:
     - compiler: gcc
       addons:
         apt:
-          sources: ['ubuntu-toolchain-r-test']
           packages: ['g++-4.8']
       env:
         - CXX=g++-4.8
 
     - compiler: gcc
       addons:
         apt:
-          sources: ['ubuntu-toolchain-r-test']
           packages: ['g++-4.9']
       env:
         - CXX=g++-4.9
 
     - compiler: gcc
       addons:
         apt:
-          sources: ['ubuntu-toolchain-r-test']
           packages: ['g++-5']
       env:
         - CXX=g++-5
 
     - compiler: gcc
       addons:
         apt:
-          sources: ['ubuntu-toolchain-r-test']
           packages: ['g++-5']
       env:
         - CXX=g++-5