Fix InvalidAccessError in IE

Okay, I've got no idea why it fails with db.version + 1, and works with
int.parse("${db.version + 1}"), but it really helps. It doesn't raise an
exception InvalidAccessError with int.parse. Probably because db.version
is like number, but somehow a little bit different, I don't know. Some
research didn't bring any answers at all...

This is how it looks in JS:

var a = J.$add$ns(t1.get$version(db), 1);
var b = H.Primitives_parseInt(H.S(J.$add$ns(t1.get$version(db), 1)), null, null);
console.log(a); // => 2
console.log(b); // => 2
console.log(typeof a); // => "number"
console.log(typeof b); // => "number"
console.log(a === b); // => true (!!!)

Anyway, it helps. So, let's merge?
Merge pull request #1 from astashov/fix-invalid-access-error-in-ie

Fix InvalidAccessError in IE