Incorrect comments in learning RNG Files

[Eliot Kimber <ekimber@contrext.com>]

Comments in learningObjectMapMod.rng and learningGroupMapMod.rng refer to
the wrong URNs.  Fix is to correct the URNs referenced in the comments to
reflect the URN for the file itself. This is a nonmaterial change that
cannot affect functioning of the grammar files in any DITA-defined way.

Cheers,

E.
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Eliot Kimber, Owner
Contrext, LLC
http://contrext.com