get_dofs broken in 06_elasticity

[gdmcbain]

fenics-tuto-in-skfem/06_elasticity/st06_elasticity.py

Line 27 in f10fc31

clamped = basis.get_dofs(lambda x, y, z: x==0.).all()

indirectly raises

TypeError: <lambda>() missing 2 required positional arguments: 'y' and 'z'

[gdmcbain]

This is kinnala/scikit-fem#51.

[gdmcbain]

Will be fixed by fa58049.

[gdmcbain]

Fixed by #9.