Hello! Great project.

To jump right in, it is a hacky experience to create an axios client for a single-endpoint API that also uses a file extension. ie `https://coolapi.com/api.php`

All url requests make their way through `combineURLs.js`, to be appended with a `/` regardless of if there was a relative url attached to the client's request config.

The current hack (it feels like hack...) to get around this is to add a request interceptor to remove the ending slash. I'm currently doing this in a project.

Happy to PR this issue with a fix to combineURLs - but I want to run it past owners first for validity.

Cheers! ✨ 
lib/helpers/combineURLs.js
'use strict';
/**
 * Creates a new URL by combining the specified URLs
 *
 * @param {string} baseURL The base URL
 * @param {string} relativeURL The relative URL
 * @returns {string} The combined URL
 */
module.exports = function combineURLs(baseURL, relativeURL) {
  return baseURL.replace(/\/+$/, '') + '/' + relativeURL.replace(/^\/+/, '');
};