docs: document apiEndpoint over servicePath (#215)

Author: JustinBeckwith

packages/google-cloud-oslogin/src/v1beta/os_login_service_client.js

@@ -54,7 +54,7 @@ class OsLoginServiceClient {
    *     your project ID will be detected automatically.
    * @param {function} [options.promise] - Custom promise module to use instead
    *     of native Promises.
-   * @param {string} [options.servicePath] - The domain name of the
+   * @param {string} [options.apiEndpoint] - The domain name of the
    *     API remote host.
    */
   constructor(opts) {