Fixed CI.

.travis.yml

@@ -6,11 +6,17 @@ matrix:
     - compiler: clang
       os: osx
 
-before_install:
-  - if [ "$CXX" == "g++" ]; then sudo add-apt-repository -y ppa:ubuntu-toolchain-r/test; sudo apt-get update -qq; fi
-
 install:
-  - if [ "$CXX" = "g++" ]; then sudo apt-get install -qq g++-4.8; fi
+  - if [ "$CXX" = "g++" ]; then export CXX="g++-4.8" CC="gcc-4.8"; fi
+
+addons:
+  apt:
+    sources:
+    - ubuntu-toolchain-r-test
+    packages:
+    - gcc-4.8
+    - g++-4.8
+    - clang
 
 script:
   make test