Incorrect minification of return [...iter].length in babili 0.1.4

[AshleyScirra]

Minifying this in babili 0.1.4:

function foo()
{
	return [...iter].length;
}

incorrectly outputs this:

function foo() {
	return 1;
}

Babili can't tell at compile-time how many elements the iterator will return, so it's incorrect to assume it's always 1.

[boopathi]

/cc @j-f1