update method name to start webkit sounds

Fix critical bug causing JS error in newest Chrome.

Chrome v.36 no longer supports the `noteOn` method, so replace it with
the newer `start` method.
See following reference:

https://code.google.com/p/chromium/issues/detail?id=358398

https://developer.mozilla.org/en-US/docs/Web/API/Web_Audio_API/Porting_w
ebkitAudioContext_code_to_standards_based_AudioContext#Changes_to_method
s_used_to_start.2Fstop_AudioBufferSourceNode_and_OscillatorNode