Add "should of" -> "should have"

See [1] for details. There's a slight edge case probability for correct cases of
'should of', for example:

"He should, of course, have drink coffee at St. Frank."

However this is mitigated by a strict string match (i.e. no commas in between
strings)

[1]
http://www.elearnenglishlanguage.com/blog/english-mistakes/should-have-vs-should-of/
Merge pull request #5 from itsthomson/master

Add "should of" -> "should have"