Materializecss: Fix issues in svg

[why]
The glyph is extremely complex with very thin open spaces and bridges.
Obviously a conversion from some colored icon, without QC afterwards.

[how]
Remove all the small crevices, smoothen the surface carefully and make
too thin strokes a bit wider.

We still keep the Devicons goal "very crisp icons" so that no rounding
of the paths and reduction of points is used.

Related:
ryanoasis/nerd-fonts#1548

Signed-off-by: Fini Jastrow <[email protected]>