Correct installation directory of GVariant specification
548ec9f1 accidentally moved the GVariant spec to the toplevel /usr/share/doc directory, which is surely not right. Let's move it back into the glib-2.0 subdirectory.
It's debatable whether this is the best place to install the GVariant specification, since it's not part of the gi-docgen docs, but surely it's much better than not putting it in any subdirectory.
Closes #3351 (closed)
Edited by Philip Withnall