Danger should not tell PR authors to put changes in the Upcoming section of the changelog if it is a new version PR

[Samasaur1]

When making a PR to master that is not a new version, if the author has not yet updated the CHANGELOG, Danger will tell them to "Put your changes in the UPCOMING section". This is what we want. However, this same message is outputted even if the PR is for a new version (in which case everything in the UPCOMING section, along with any new information, should be under a version heading).

Here's the part of the Dangerfile that controls this output:

DiceKit/Dangerfile.swift

Lines 92 to 101 in b91141b

	// MARK: Changelog updated
	if editedFiles.contains("CHANGELOG.md") {
	message("The CHANGELOG was updated")
	} else {
	if FileManager.default.fileExists(atPath: "CHANGELOG.md") {
	fail("The CHANGELOG was not updated! (put your changes in the UPCOMING section)")
	} else {
	warn("There is no CHANGELOG!")
	}
	}

We should put these CHANGELOG checks inside the if-else statement checking new versions, in order to give more useful output.