Bind "this" on API class methods

[nowlena]

I'm having an issue using the stencil-utils/src/api/product.js aka utils.api.product.getById method because of the "this" keyword.

Please bind(this) on all class methods to keep scope in order.

/**
 * FOR EXAMPLE 
 * after this line: https://github.com/bigcommerce/stencil-utils/blob/master/src/api/product.js#L13
 * add the following code
 */
this.getById = this.getById.bind(this);

This will prevent any issues with this referring to some outside Class