Lexer is grouping `n1 <- n2` (a likely typo) as `n1 < -n2`

[tnelson]

Minimum example:

#lang forge
sig Person { age: one Int }
test expect {
    parsing: {all p: Person | (p.age <- 17) iff (p.age < -17)} is theorem
}

This test passes in 2.8.0. My expectation was that it would produce a parser error, since <- isn't a valid token in that position. (This example was extracted from a real typo made by a real user.)

[tnelson]

Resolved by the above PR