Sine example produces 220hz, not 440hz

Tested by running the sine.js example, but the resulting tone sounds like 220hz, not 440hz as documented.

Changing the channels to 1 seems to correct the result, but any other value for the channel  generates a non-440hz tone. I don't think you need to divide the angle by the number of channels, however I'm unsure of this math.

Ref:
https://www.youtube.com/watch?v=OUvlamJN3nM 440hz tone
https://www.youtube.com/watch?v=82HaIjTq0yk 220hz tone
Merge pull request #38 from jproulx/patch-1

Sine example produces 220hz, not 440hz