update to gcc-5

.travis.yml

@@ -16,9 +16,9 @@ install:
   # version is the same.
   - sudo add-apt-repository -y ppa:ubuntu-toolchain-r/test
   - sudo apt-get -qq update
-  - sudo apt-get -qq install g++
-  - sudo apt-get -qq install gcc
-  # - export CXX="g++-5" CC="gcc-5"
+  - sudo apt-get -qq install g++-5
+  - sudo apt-get -qq install gcc-5
+  - export CXX="g++-5" CC="gcc-5"
   - wget https://repo.continuum.io/miniconda/Miniconda3-latest-Linux-x86_64.sh -O miniconda.sh
   - bash miniconda.sh -b -p $HOME/miniconda
   - export PATH="$HOME/miniconda/bin:$PATH"