update "Starting development of the next version" in DEVELOPERS.md
The "returning to the development series" wording was a remnant from
when stable releases had even minor versions and development versions
had odd minor versions. There no longer are different stable and
development series so there's nothing to return to. We always go
forward. The development versions have the same version number as the
tentative next stable release version, with a ~dev suffix.
projects / graphviz / commit