added python3-pyqt4 package in .travis.yml

.travis.yml

@@ -9,6 +9,7 @@ python:
 
 install:
   - sudo apt-get update
+  - sudo apt-get install python3-pyqt4
   # We do this conditionally because it saves us some downloading if the
   # version is the same.
   - wget https://repo.continuum.io/miniconda/Miniconda3-latest-Linux-x86_64.sh -O miniconda.sh;
@@ -22,7 +23,7 @@ install:
 
   - conda create -q -n test-environment python=$TRAVIS_PYTHON_VERSION pytest pytest-cov
   - source activate test-environment
-  - conda install numpy scipy netcdf4 pyqt
+  - conda install numpy scipy netcdf4
   - conda install pyproj matplotlib bokeh jupyter ipywidgets
   - python setup.py install