contain text assertion does not work if String.prototype.includes is not available

[rincedd]

The following breaks in environments that do not support the ES2015 method String.prototype.includes, such as Internet Explorer and Phantom JS.

expect(wrapper.find('#child')).to.contain.text('Te')

I guess the solution would be to include an appropriate polyfill in the build.

[ayrton]

Closely related to https://github.com/producthunt/chai-enzyme/pull/111

[ayrton]

Merged in #111 so this will no longer be an issue on the next release

[rincedd]

Thanks :+1: