Checks if flag is that of negation.

@example --no-force >> true
@example --force >> false

@param val the value to inspect.
@param negate the negation char to check if exists.
function isNegateFlag(val, negate) {
    negate = escape(negate || constants_1.NEGATE_CHAR);
    return (new RegExp('^--' + negate)).test(val);
}