Bikeshed update for 'Update definition of scrollSource to allow it to be null (w3c#34)

This should fix w3c#11, w3c#12, and w3c#13.
' [ci skip]

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commit bf1a16b
Author: Stephen McGruer <stephen.mcgruer@gmail.com>
Date:   Mon Nov 26 10:23:54 2018 -0500

    Update definition of scrollSource to allow it to be null (w3c#34)

    This should fix w3c#11, w3c#12, and w3c#13.

Author: stephenmcgruer