Set backend to Agg in matplotlibrc; Build on linux.

Author: mcflugen

.travis.yml

@@ -6,8 +6,9 @@ env:
   global:
     - CONDA_PREFIX=$HOME/miniconda
     - MINICONDA_URL_BASE="https://repo.continuum.io/miniconda/Miniconda3-latest"
+    - MPLCONFIGDIR=$HOME/.config/matplotlib
 os:
-  # - linux
+- linux
 - osx
 sudo: false
 before_install:
@@ -35,6 +36,7 @@ install:
 - conda install landlab jupyter -c landlab
 - conda info -a && conda list
 script:
+- mkdir -p $MPLCONFIGDIR && echo "backend: Agg" > $MPLCONFIGDIR/matplotlibrc
 - ./run-all-tests.sh
 virtualenv:
   system_site_packages: false