Need to explicitly install matplotlib as well for travis.

Author: WeatherGod

.travis.yml

@@ -3,6 +3,7 @@ sudo: false
 env:
   global:
     - NUMPY=numpy
+    - MPL=matplotlib
     - TEST_ARGS=--no-pep8
 
 language: python
@@ -30,6 +31,7 @@ install:
     pip install --upgrade pip
     pip install --upgrade setuptools
     pip install $NUMPY
+    pip install $MPL
   - |
     cd geos-3.3.3
     export GEOS_DIR=$HOME/.local/