Enumerable#every and #some should always return booleans

Batman's `#every` and `#some` methods do not correctly implement the ES5 specifications for the matching native array methods. While the specifications state that these methods should always return booleans, Batman's versions will return the last truthy value.

`Array#every`: http://www.ecma-international.org/ecma-262/5.1/#sec-15.4.4.16
`Array#some`:  http://www.ecma-international.org/ecma-262/5.1/#sec-15.4.4.17