Rename EndingTypes to EndingType or EndingsType

[inexorabletash]

Sorry, missed this during the review.

The EndingTypes enum is named with a plural which doesn't make sense when used in the dictionary:

dictionary BlobPropertyBag {
  DOMString type = "";
  EndingTypes endings = "transparent";
};

There's only one type so the property type shouldn't be types.

Either EndingType or EndingsType makes more sense.

[mkruisselbrink]

Ah yes. I shouldn't have blindly copied the old spec. Either sounds good to me.