docs: Document errors property on getEntries response

Fixes #69

lib/entities/entry.js

@@ -30,6 +30,7 @@ export function wrapEntry (data) {
  * @prop {number} skip
  * @prop {number} limit
  * @prop {Array<Entities.Entry>} items
+ * @prop {Array<Object>=} errors - Array of errors that might occur when retrieving entries.
  * @prop {function(): Object} toPlainObject() - Returns this Entry collection as a plain JS object
  * @prop {function(?function=, space=): Object} stringifySafe(replacer,space) - Stringifies the entry collection, accounting for circular references. Circular references will be replaced with just a Link object, with a <code>circular</code> property set to <code>true</code>. See <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify">MDN</a> and <a href="https://www.npmjs.com/package/json-stringify-safe">json-stringify-safe</a> for more details on the arguments this method can take.
  */