Readme file: consider to remove reference to WordPress 2.7

[afercia]

In the readme.html file, under the section "Updating" there's a reference to WordPress 2.7. It mentions the "single click" automatic updater for major versions available in the Updates page (see attached screenshot).

While it makes perfectly sense to explain what the updating options are, the reference to 2.7 sounds a bit old and maybe it could be removed. At the time of writing this ticket, WordPress is at version 5.2 and 5.3 is going to happen soon. I'd like to propose to change the sentence:

If you are updating from version 2.7 or higher, you can use the automatic updater:

to:

To use the automatic updater:

[donmhico]

I agree @afercia. Version 2.7 is no longer in the radar based on the stats - ​https://wordpress.org/about/stats/.

[davidbaumwald]

With 5.3 Beta 1 shipping today, I’m punting this to Future Release so as not to clog up the 5.4 milestone. However, @afercia, feel free to move to 5.4 if you feel comfortable committing to resolving this fully then... thanks!

[SergeyBiryukov]

In 47056:

Docs: Remove a reference to WordPress 2.7 from readme.html.

Props afercia, donmhico.
Fixes #47963.