Change .travis.yml to include pyparsing

.travis.yml

@@ -11,6 +11,7 @@ install:
 - pip install coveralls
 - pip install Sphinx==1.3.2
 - pip install travis-sphinx
+- :pip install pyparsing
 script:
 - coverage run --source=cadquery ./runtests.py
 - travis-sphinx --nowarn --source=doc build