replace transform.Matrix with Point in gmsh reader

This patch replaces `transform.Matrix` with the recently introduced
`transform.Point` in the `gmsh` reader.

nutils/mesh.py

@@ -550,7 +550,7 @@ def simplex(nodes, cnodes, coords, tags, btags, ptags, name='simplex', *, space=
 
   pgroups = {}
   if ptags:
-    ptrans = [transform.Matrix(linear=numpy.zeros(shape=(ndims,0)), offset=offset) for offset in numpy.eye(ndims+1)[:,1:]]
+    ptrans = [transform.Point(offset) for offset in numpy.eye(ndims+1)[:,1:]]
     pmap = {inode: numpy.array(numpy.equal(nodes, inode).nonzero()).T for inode in set.union(*map(set, ptags.values()))}
     for pname, inodes in ptags.items():
       ptransforms = transformseq.PlainTransforms([topo.transforms[ielem] + (ptrans[ivertex],) for inode in inodes for ielem, ivertex in pmap[inode]], ndims, 0)