Add support for moment >= 2.25

[jeffmhastings]

In moment 2.25.0 they added support for YYYY as a valid ISO_8601 date. This causes waterline-sqlite3 to convert 4 digit strings into Dates, which can cause unintended consequences with the way that waterline-sqlite3 works.

For instance, with a string like '1234', it will be stored in the database as -23225875200000(number of milliseconds before 1970, I believe).

$ node --eval "console.log(new Date('1234').valueOf())"
-23225875200000

This is inconsistent with the way that waterline-sqlite3 works with moment < 2.25, which would not consider '1234' to be a valid date. In order to support these newer version of moment without breaking backwards compatibility (and without introducing much larger changes) we can simply skip parsing the date for strings less than or equal to 4 characters in length.