Add wiktionary to dictionary APIs.

README.md

@@ -549,6 +549,7 @@ API | Description | Auth | HTTPS | CORS |
 | [OwlBot](https://owlbot.info/) | Definitions with example sentence and photo if available | `apiKey` | Yes | Yes |
 | [Oxford](https://developer.oxforddictionaries.com/) | Dictionary Data | `apiKey` | Yes | No |
 | [Synonyms](https://www.synonyms.com/synonyms_api.php) | Synonyms, thesaurus and antonyms information for any given word | `apiKey` | Yes | Unknown |
+| [Wiktionary](https://wiktionary.org/w/api.php) | Collaborative dictionary data | No | Yes | Yes |
 | [Wordnik](https://developer.wordnik.com) | Dictionary Data | `apiKey` | Yes | Unknown |
 | [Words](https://www.wordsapi.com/docs/) | Definitions and synonyms for more than 150,000 words | `apiKey` | Yes | Unknown |