Auto save indicator on published post looks like post has been updated

[kriskarkoski]

Describe the bug
When editing a published post, the auto save visual indicator of "Updating" on the Update button is identical to when the post is actually updated, causing confusion that any updates have been published when they are not until Update is manually clicked.

To Reproduce
Steps to reproduce the behavior:

1. Edit a published post
2. Make a change to the content
3. Wait for an auto save to occur within a few seconds
4. Note the visual indication of the auto save on the Update button is identical to when the post is actually updated

Expected behavior
A clear indication that the change was auto saved (already included) without the confusing updated message that causes confusion that the public post has been updated when it has not.

Screenshots

Keeping the existing autosave message while making the Update button unavailable (but not changing the text to Updating as it is) should make this work more clearly.

Desktop (please complete the following information):

• OS: OS X 10
• Browser Chrome 66

Additional context
Gutenberg 3.0.1

[danielbachhuber]

Potentially related #7218 #7135