Having "-" as literall match thingies causes invalid escape sequences to be generated when using the unicode

[TheGrandmother]

If i have the following token defined:
ARITHMETIC: ['+' , '-'],
And all my regular expressions are using the u flag moo will output an an invalid regex escape sequence as \- is apparently uncool when rolling with the u flag.
Changing the token definition to:
ARITHMETIC: ['+' , /-/u], works but is not pretty.

moo version 0.5.1
Node version 13.14.0

[tjvr]

Ooh, that's surprising!

[nathan]

@tjvr simplest fix is to escape - as \x2d (which works everywhere) instead of \- (which only works inside [] in Unicode mode, even under Annex B).

It's incomprehensible why TC39 decided to make the RegExp grammar this inconsistently nitpicky (e.g., \{ works fine inside a Unicode character class even though the backslash does nothing).

[tjvr]

If someone wants to raise a PR which updates reEscape (or whatever the function’s called), that would be great.

[fabiosantoscode]

I've worked around this by simply changing '-' to /-/u, putting this out here in case it's helpful.