Add boolean support to jquery attr() definition

Add support for booleans to jquery attr()
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In its current state the jQuery TypeScript definition can't compile things like this:

    $('#someInput').attr('disabled', true);

despite being valid. Workarounds like `true.toString()` compile but aren't functionally homogenous.

This adds an overload: `attr(attributeName: string, value: boolean)`

Errors this fixes:

>Supplied parameters do not match any signature of call target:
>	Could not apply type 'string' to argument 2 which is of type 'boolean'.
>Could not select overload for 'call' expression.
>Supplied parameters do not match any signature of call target.