Bump json-schema version

[ForsakenHarmony]

For webpack compatibility

[davepacheco]

Thanks! I hope you don't mind that I incorporated your change with a few changes to the commit:

• reformatted the commit message to reflect the convention in this repository
• updated version in package.json in prep for a new jsprim release
• updated CHANGES.md for new release

I verified that there do not appear to be any breaking changes in the new json-schema version and
I ran the test suite using Node 0.10.43 and 0.12.7 on illumos.

I've published jsprim@1.3.1 with this change.

Thanks again!

[davepacheco]

This addresses #13 via commit 825aba4.

[ForsakenHarmony]

np, thx for the update