Bundled Themes: Bump theme versions ahead of WordPress 5.5.

The following theme versions will be released in coordination with WordPress 5.5:
- Twenty Ten: 3.1
- Twenty Eleven: 3.5
- Twenty Twelve: 3.2
- Twenty Thirteen: 3.1
- Twenty Fourteen: 2.9
- Twenty Fifteen: 2.7
- Twenty Sixteen: 2.2
- Twenty Seventeen: 2.4
- Twenty Nineteen: 1.7
- Twenty Twenty: 1.5

Props whyisjake, desrosj.
Reviewed by whyisjake, SergeyBiryukov, desrosj.
Merges [48775] to the 5.5 branch.
Fixes #50889.
Built from https://develop.svn.wordpress.org/branches/5.5@48776


git-svn-id: https://core.svn.wordpress.org/branches/5.5@48538 1a063a9b-81f0-0310-95a4-ce76da25c4cd