[Tests] trying an alternative syntax for gcc upgrades

.travis.yml

@@ -1,17 +1,20 @@
 language: generic
 sudo: required
 addons:
+  apt:
+    sources:
+      - ubuntu-toolchain-r-test
+    packages:
+      - gcc-4.8
+      - g++-4.8
   apt_packages:
-  - zsh
-  - ksh
+    - zsh
+    - ksh
 cache:
   directories:
     - $HOME/.stack
     - $TRAVIS_BUILD_DIR/.cache
 before_install:
-  - sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y
-  - sudo apt-get update -q
-  - sudo apt-get install gcc-4.8 -y
   - $SHELL --version 2> /dev/null || dpkg -s $SHELL 2> /dev/null || which $SHELL
   - curl --version
   - wget --version