refactor: use positive lookahead in RegExp

[noscripter]

Since negative lookbehind is relatively new(which got accepted in ECMAScript in 2018) and only v8 and node.js behind v9 without a flag support it, it's more convenient and compatible to use positive lookahead instead.

ref: https://stackoverflow.com/questions/641407/javascript-negative-lookbehind-equivalent

[jonschlinkert]

it's more convenient and compatible to use positive lookahead instead.

It doesn't do the same thing. Lookahead and lookbehind don't advance the cursor position, as they're "zero-length" assertions. Thus, (?:[^`]) would return a false-negative at the beginning of the string.

However, I'm glad you brought this up, I'd like to make the regex more compatible. I'll keep this open to discuss. Perhaps we should add some test cases to make sure it works in different scenarios.

[jonschlinkert]

and thank you for the PR!