Wrong name for window, should be GRASS not GDAL

row 117:  immediate right of :guilabel:`View output`), then close the :guilabel:`GDAL
row 118 : Tools` window.

Lesson is about GRASS, not about GDAL. The window that is opened is the "GRASS Tools" window,
not the "GDAL Tools" window.
Merge pull request #348 from DiGro/patch-2

Wrong name for window, should be GRASS not GDAL