Ensure Float64Array is supported

I encountered an issue while using this (awesome) library where `Float32Array` was supported while `Float64Array` was not. Specifically, in my headless Phantom.js integration tests. [See this issue](https://code.google.com/p/phantomjs/issues/detail?id=607&can=1&q=Float64Array)

I'm unsure how to run the tests for this library so apologies for not being able to check that, but this simple fix appears to be working just fine :guitar: :saxophone: