logic issue in TapDelay::setTapDelays() 

The `setTapDelays()` method in `TapDelay` takes in a vector of **unsigned longs**:
`void TapDelay :: setTapDelays( std::vector<unsigned long> taps )`

[On line 71](https://github.com/thestk/stk/blob/master/src/TapDelay.cpp#L71), we have this if-statement:
`if ( taps[i] < 0 ) {`

but isn't this always false if the `taps` array only has *unsigned* longs?