Refine tab bar settings UI string
Summary:
Make the Qt 5.9 sentence present tense since we already
passed that version, and add a minor grammar update.
Reviewers: Konsole, hindenburg
Reviewed By: Konsole, hindenburg
Subscribers: ngraham, hindenburg, konsole-devel
Tags: Konsole
Differential Revision: https://phabricator.kde.org/D13125