Bugfix: PitchDetection returning the wrong pitch (#187)

When converted to the current syntax, the operation was the wrong way around.
See https://github.com/marl/crepe/blob/gh-pages/crepe.js#L141 for the original.

src/PitchDetection/index.js

@@ -79,7 +79,7 @@ class PitchDetection {
  const productSum = products.dataSync().reduce((a, b) => a + b, 0);
  const weightSum = weights.dataSync().reduce((a, b) => a + b, 0);
  const predictedCent = productSum / weightSum;
- const predictedHz = 10 * ((predictedCent / 1200.0) ** 2);
+ const predictedHz = 10 * (2 ** (predictedCent / 1200.0));
 
  const frequency = (confidence > 0.5) ? predictedHz : null;
  this.frequency = frequency;