Make plugin work well in non node environments

[nmantulenko]

I use this module with react-native.
And I have to install assert lib independently to be able to work with it

Shouldn't we just put 'assert' in package.json's dependencies?

[neilbmclaughlin]

Apologies for the delay in responding.

I think we probably shouldn't be using assert in the first place. It could be easily rewritten to remove it while still validating the passed parameters.

I'll make some changes with a view to raising a PR.