updated travis for graphviz

Author: jacobwilliams

.travis.yml

@@ -64,6 +64,7 @@ install:
       rm f90split.f90
     fi
   - pip install --upgrade pygooglechart
+  - pip install --upgrade graphviz
   - (pip install --upgrade FoBiS.py && FoBiS.py --version)
   - (pip install --upgrade ford && ford --version)
   - (pip install --upgrade git+https://github.com/dmeranda/demjson.git && jsonlint --version)