Add .prettierignore extension

Author: andreoliwa

identify/extensions.py

@@ -269,6 +269,7 @@
     '.mention-bot': EXTENSIONS['json'] | {'mention-bot'},
     '.npmignore': {'text', 'npmignore'},
     '.pdbrc': EXTENSIONS['py'] | {'pdbrc'},
+    '.prettierignore': {'text', 'gitignore'},
     '.pypirc': EXTENSIONS['ini'] | {'pypirc'},
     '.rstcheck.cfg': EXTENSIONS['ini'],
     '.yamllint': EXTENSIONS['yaml'] | {'yamllint'},