MIN: Added a specific version number for Shpnix in requirements file.
MIN: Added a specific version number for Shpnix in requirements file.

The new requirements.txt specify 1.2.3 as Sphinx version. This is because it
turned out that newer Sphinx versions caused problems on Codeship.

heistermann/wradlib,heistermann/wradlib,wradlib/wradlib,kmuehlbauer/wradlib,wradlib/wradlib,kmuehlbauer/wradlib