update to include negative signal

.travis.yml

@@ -6,21 +6,18 @@ python:
 sudo: false
 addons:
   apt:
-    source:
-      - ubuntu-toolchain-r-test
     packages:
       - libblas-dev
       - liblapack-dev
       - gfortran
-      - g++-5
-      - gcc-5
-env:
-  - MATRIX_EVAL="CC=gcc-5 && CXX=g++-5"
-before_install:
-  - eval "${MATRIX_EVAL}"
 install:
   # We do this conditionally because it saves us some downloading if the
   # 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++-4.8
+  - sudo apt-get -qq install gcc-4.8
+  - export CXX="g++-4.8" CC="gcc-4.8"
   - 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"