KDE Plasma Desktop: update to 5.18.2

Tuesday, 25 February 2020. Today KDE releases a bugfix update to KDE Plasma 5,
versioned 5.18.2. Plasma 5.18 was released in February 2020 with many feature
refinements and new modules to complete the desktop experience.

This release adds a week's worth of new translations and fixes from KDE's
contributors. The bugfixes are typically small but important and include:

• Discover: fix build on old flatpak versions.
• Unify KSysGuard cpu clock speed names.
• Emojier: improve the fallback mechanism to detect languages.

Full changelog:
https://kde.org/announcements/plasma-5.18.1-5.18.2-changelog.php