CustomDeclarationOrderCheck: Correct spelling of DeclareAnonClassField

[jsoref]

To date, the annotation is DeclareAnnonClassField(...), but conceptually, it's trying to describe "declare an anonymous class field", the proper abbreviation for anonymous should be anon, not annon (which would be an abbreviation for annonymous [sic]), and thus the correct annotation should be DeclareAnonClassField(...).

Migration for users

If you use DeclareAnnonClassField in your configuration for this Check, please rename it to DeclareAnonClassField.

[rnveach]

@jsoref This doesn't explain anything like name of check being affected and why it is being renamed.
Please update issue and title to be more descriptive.

[romani]

@jsoref, please explain users how to migrate, what they should change in theirs config file. In your commit you have example, just place it to description

[rnveach]

I added migration section.

[romani]

fix is merged