Fix package requires

The phasefield model requires the generation of a module by Cython. However, this file was not shipped with pypi and cython is not required by lbmpy.

setup.py

@@ -83,7 +83,8 @@ setup(name='lbmpy',
       url='https://i10git.cs.fau.de/pycodegen/lbmpy/',
       packages=['lbmpy'] + ['lbmpy.' + s for s in find_packages('lbmpy')],
       install_requires=['pystencils', 'sympy>=1.2', 'numpy>=1.11.0'],
-      package_data={'lbmpy': ['phasefield/simplex_projection.pyx']},
+      package_data={'lbmpy': ['phasefield/simplex_projection.pyx',
+                              'phasefield/simplex_projection.c']},
       ext_modules=cython_extensions("lbmpy.phasefield.simplex_projection") if USE_CYTHON else [],
       classifiers=[
           'Development Status :: 4 - Beta',