CompatHelper: bump compat for "StatsBase" to "0.34"

[github-actions[bot]]

This pull request changes the compat entry for the StatsBase package from 0.33.5 to 0.33.5, 0.34.

This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry. It is your responsibility to make sure that your package tests pass before you merge this pull request.

[palday]

@namilan I went to bump the version here and then I remembered that we currently have Technically Breaking changes on master and are saving up for a 2.0 release, so I changed the version to 2.0-DEV. I'll make a compat PR against the v1 branch

[andreasnoack]

Superseded by #531