v6.0.0: Generate stubs for WordPress 6.0.0 (#35)

* updated to wp6.0.0

* Add blank line back to end of composer.json in source dir. Moved v6 to new line in release-latest-versions.sh

* Add blank line back to end of composer.json in source dir. Moved v6 to new line in release-latest-versions.sh

v5.9.3

Generate stubs for WordPress 5.9.3

v5.9.2

Generate stubs for WordPress 5.9.2

v5.8.4

Generate stubs for WordPress 5.8.4

v5.7.6

Generate stubs for WordPress 5.7.6

v5.6.8

Generate stubs for WordPress 5.6.8

v5.5.9

Generate stubs for WordPress 5.5.9

v5.4.10

Generate stubs for WordPress 5.4.10

v5.3.12

Generate stubs for WordPress 5.3.12