Typeahead does not URI encode query for async source

[martijnluinstra]

Version & browser

0.21.3

Which component

Typeahead

Steps to reproduce the problem

Type an '&' in a typeahead input field.

Expected behavior

Queries async source for items containing the string '&'

Actual behavior

Queries async source for items containing the string ''

Should be easy to fix by URI encoding the querystring