could lark.lark be missing "\" end of line things

[hbusul]

Describe the bug

I was trying to parse a lark file using the lark.lark file provided in the repo, and I realized it does not like:

function: "ABS"i | "ARCTAN"i | "CEIL"i | "COS"i | "ERRORF"i | "EXP"i | "FLOOR"i |\
          "LOG"i | "LOG10"i | "MAPVAL"i | "MAX"i | "MIN"i | "MOD"i | "NORMAL"i

I understand it is not a biggie since lark is not bootstrapped,

To Reproduce

Get lark.lark

Save this dummy grammar to parse_me.lark

start: (function? _NL)* function?
_NL: /(\r?\n)+\s*/
function: "ABS"i | "ARCTAN"i | "CEIL"i | "COS"i | "ERRORF"i | "EXP"i | "FLOOR"i |\
          "LOG"i | "LOG10"i | "MAPVAL"i | "MAX"i | "MIN"i | "MOD"i | "NORMAL"i

Then parse it using lark.lark

from lark import Lark

with open("lark.lark", "r") as f:
    lark_grammar = f.read()

parser = Lark(lark_grammar)

with open("parse_me.lark", "r") as f:
    problem = f.read()

parsed_problem = parser.parse(problem)

You will get

lark.exceptions.UnexpectedCharacters: No terminal matches '\' in the current parser context, at line 3 col 82

"COS"i | "ERRORF"i | "EXP"i | "FLOOR"i |\
                                        ^
Expected one of: 
	* LSQB
	* TOKEN
	* __ANON_0
	* _VBAR
	* RULE
	* LPAR
	* REGEXP
	* _NL
	* STRING

Finding and replacing backward slash followed by a new line with "", is my current workaround, but probably lark.lark file needs to be updated.