fix docs for Vector.angle, closes #471

src/geometry/Vector.js

@@ -214,7 +214,7 @@ module.exports = Vector;
  };
 
  /**
- * Returns the angle in radians between the two vectors relative to the x-axis.
+ * Returns the angle between the vector `vectorB - vectorA` and the x-axis in radians.
  * @method angle
  * @param {vector} vectorA
  * @param {vector} vectorB