Fix strange bug with regexes

[gilbert]

For some reason the regex isn't isn't updating x as it should.
I tried isolating, but no luck.
This fix is a bit more code, but it's good according to the spec,
so there should be no issues with backwards compatibility.

[stevemao]

What exactly does it fix? Where is the updated test?

[gilbert]

lastIndex updated as it should after one .exec() call, but afterwards reset to 0.

I will add a test when I get the chance. I just wanted to throw this up before I forgot about it.

[jaruba]

regular expressions don't work for me with or without this change..

I get:

Uncaught TypeError: Expected a string
at: node_modules\escape-string-regexp\index.js:7

this happens with the regex examples in README.md too.

[stevemao]

@jaruba This will be merged once a test has been added.

[stevemao]

@mindeavor can you add a test?