Bump version to 19.0
Bump version to 19.0

rouge8/pip,xavfernandez/pip,pradyunsg/pip,xavfernandez/pip,rouge8/pip,pfmoore/pip,pfmoore/pip,xavfernandez/pip,sbidoul/pip,pypa/pip,pypa/pip,rouge8/pip,pradyunsg/pip,sbidoul/pip