Incorrect subtitle for parrot imitating elder guardian (fix in description)

Relates to MC-133013. Discovered while testing MC-141221.

The subtitle for parrots imitating elder guardians (in english, anyway. Haven't tested other languages) is "Parrot flaps".

How to fix

Change the following line in en_us.json from

"subtitles.entity.parrot.imitate.elder_guardian": "Parrot flaps",

to

"subtitles.entity.parrot.imitate.elder_guardian": "Parrot moans",