Fix an error related to Hammer.JS on client startup on pages that define
a global variable called `define`, which is part of Require.JS. Hammer's UMD
bundle does not set `module.exports` in this case, so modules that import it
get an empty object back.

Fix the issue by making sure that any reference to `define` inside
bundles evaluates to undefined (assuming there is no local variable
within the module with that name).

This fixes an issue where clicking "Annotate" failed to open the sidebar
on BBC News articles (eg. https://www.bbc.co.uk/news/world-52144390).