extension synonyms yml and yaml

[bogdanvlviv]

Add extension synonyms yml and yaml for MIME type application/x-yaml.

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[bogdanvlviv]

r? @rafaelfranca

[rafaelfranca]

The bot assigned this to someone else so unless you have a good reason to change please don't change it. As there is no reason to you assign it to me I'll revert it.

[egilburg]

should .xml extension likewise be registered?

also, perhaps refactor Mime::Type.register API to use kwargs? (with deprecated current form)

[rafaelfranca]

.xml extension is already registered no?

[egilburg]

If it is nevermind, just not clear from this line Mime::Type.register "application/xml", :xml, %w( text/xml application/x-xml ) as it's not passed as the extension argument.

[rafaelfranca]

you only need to pass the extension argument if you want to create aliases.

[bogdanvlviv]

@matthewd, can be merged this pull request or i should close it?