fix #715, we can obtain the shape of a Cm05Matrix

[AmirMardan]

In this PR, I fix a minor issue that exists for obtaining the shape of a Cm05Matrix, issue #715

Without this PR, running the following script

import pygimli as pg

# No matter what mesh
A = pg.utils.covarianceMatrix(mesh, I=5)
cm05 = pg.matrix.createCm05(A)

print(cm05.shape)

throws

return self.row()
           ^^^^^^^^
AttributeError: 'Cm05Matrix' object has no attribute 'row'

Accepting this PR, this error will be fixed

fix #715