Add config option to override Express' default request size limit

[bdcarr]

Hello! I've been using your package to parallelise some test scripts. One of them creates ~300kb of data that needs caching, which resulted in Error: request entity too large, which I found was coming from Express, which has a default limit of 100kb.

This change lets you increase that limit:

globalCache.config({
  limit: '10mb',
});

export default globalCache.wrap(config);

With that, caching works in my test.

limit isn't a very helpful name imo, but I couldn't think of something succinct and enlightening so I just copied what it's called in express.

I published my fork here, just so my team can use it until this PR is accepted, so if you want to try it out, there it is. Immediately after doing that I learned about patch-package. Oh well.