Does not fail for renderFileAsync

[calebeby]

I assume this problem applies to all *Async methods, but I only tested renderFileAsync

When the actual output does not match the expected output, it prints an UnhandledPromiseRejectionWarning: Unhandled promise rejection..., but the tests still pass, even though they obviously shouldn't.

Try changing the expected output in https://github.com/jstransformers/jstransformer-rollup