Add zip to formats

[huard]

Overview

Added FORMATS.ZIP.

Related Issue / Discussion

Fix #459

Contribution Agreement

(as per https://github.com/geopython/pywps/blob/master/CONTRIBUTING.rst#contributions-and-licensing)

• I'd like to contribute [feature X|bugfix Y|docs|something else] to PyWPS. I confirm that my contributions to PyWPS will be compatible with the PyWPS license guidelines at the time of contribution.
• I have already previously agreed to the PyWPS Contributions and Licensing Guidelines

[coveralls]

Coverage decreased (-0.1%) to 75.092% when pulling 049740c on huard:fix-459 into 2a8d9ee on geopython:master.

[coveralls]

Coverage decreased (-0.1%) to 75.092% when pulling 049740c on huard:fix-459 into 2a8d9ee on geopython:master.

[cehbrecht]

looks good.