Fix content length in proxy.js when response from server sends it as a string

[jesseditson]

Like the title says - this one line fix will make proxying to servers that don't send an int as content-length work.

[ljharb]

hmm - it looks like lib/proxy doesn't exist anymore, and there's nothing currently setting content-length - the closest i could find was https://github.com/substack/testling/blob/master/bin/cmd.js#L159.

I know it's been a very long time, but do you know if the same issue is still happening?

[jesseditson]

Reading #27 it looks like the issue was that trying to use testling example/localhost.js --browser=chrome was failing - however it's been far too long for me to shed any more light than what's in the issue.

Happy to close this one out in the meantime, thanks for taking the reins on this repo!