Update library for detection of legacy user agents

Inclues the fixes from https://github.com/slightlyoff/suchi.js/issues/14, which resolved
some IE9 issues reported by our users
Merge pull request #415 from alphagov/update-legacy-browser-check

Update library for detection of legacy user agents

Inclues the fixes from slightlyoff/suchi.js#14, which resolved
some IE9 issues reported by our users.