Add .json extension for application/jf2feed+json

[binyamin]

If this is good to go, I can open a PR

mime-db/src/iana-types.json

Lines 1028 to 1032 in c9242a9

	"application/jf2feed+json": {
	"sources": [
	"https://www.iana.org/assignments/media-types/application/jf2feed+json"
	]
	},

[binyamin]

Note that .jf2 is used as well, although the IANA page doesn't mention it.

[dougwilson]

Hello, and thank you for the issue. I'm not sure what the implications would be for consumers of this module that attempt to build a reverse lookup (extension to type) would be. Investigation would need to be performed.