Close PRs whose title is "Master"

[cvrebert]

These are indicative of "test edit" PRs.
Refs twbs/bootstrap#18134 , among a jillion others.

[cvrebert]

Also perhaps if the title starts with "Create" or "test"
Example: twbs/bootstrap#16503
Example: twbs/bootstrap#17487

[cvrebert]

And perhaps warn if the title is ^Update WORD(\.WORD)?$

[cvrebert]

Or if the title is "Merge pull request #1 from twbs/master" (refs twbs/bootstrap#18227 , twbs/bootstrap#16889 , among others)