README.md: minor shuffle to fix the description on the npmjs.org page
README.md: minor shuffle to fix the description on the npmjs.org page

It looks like they use the first line of the README to populate the
description field on https://npmjs.org/package/jwcrypto , and previously
this first line was the travis-ci build-status IMG tag.

vladikoff/browserid-crypto,mozilla/browserid-crypto,vladikoff/browserid-crypto,mozilla/browserid-crypto,mozilla/browserid-crypto,vladikoff/browserid-crypto