Sanitise environment variables used in RegExps

[Alhadis]

The PATH and CHROME_PATH variables are currently being used verbatim for constructing a regular expression:

chrome-launcher/src/chrome-finder.ts

Lines 52 to 53 in 9aa64d6

	{regex: new RegExp(`^${process.env.HOME}/Applications/.*Chrome.app`), weight: 50},
	{regex: new RegExp(`^${process.env.HOME}/Applications/.*Chrome Canary.app`), weight: 51},

This can lead to confusing behaviour if a user's path contains RegExp metacharacters such as $ or ^. Worse still, it leaves room for a malicious actor to inject an expression guaranteed to send the process into performance hell:

export CHROME_PATH='(.*.*.*.*.*.*.*.*.*.*.*.*)*[^Bb]|$'

I also replaced stuff like `${process.env.PATH}` with simply process.env.PATH, because the former syntax will stringify an undefined value as "undefined", which probably isn't what you want (or expect).

[patrickhulce]

thanks very much, nice catch @Alhadis! 👍

[patrickhulce]

LGTM, thanks @Alhadis! 🎉