fix docstring of examples/navier_stokes/stokes_slip_bc.py
fix docstring of examples/navier_stokes/stokes_slip_bc.py

rc/sfepy,vlukes/sfepy,lokik/sfepy,BubuLK/sfepy,sfepy/sfepy,RexFuzzle/sfepy,RexFuzzle/sfepy,rc/sfepy,lokik/sfepy,lokik/sfepy,rc/sfepy,BubuLK/sfepy,lokik/sfepy,vlukes/sfepy,RexFuzzle/sfepy,RexFuzzle/sfepy,vlukes/sfepy,BubuLK/sfepy,sfepy/sfepy,sfepy/sfepy