Add libkf5windowsystem-dev to build depends.

debian/changelog

@@ -1,10 +1,14 @@
 qps (2.1.0-0ubuntu1) UNRELEASED; urgency=medium
 
+  [ Simon Quigley ]
   * New upstream release.
     - Update upstream signing key.
     - Update LXQt build dependencies.
   * Run wrap-and-sort.
 
+  [ Dan Simmons ]
+  * Added libkf5windowsystem-dev to build dependendies.
+
  -- Simon Quigley <tsimonq2@ubuntu.com>  Fri, 01 May 2020 00:02:11 -0500
 
 qps (2.0.0-1ubuntu2) groovy; urgency=medium

debian/control

@@ -6,6 +6,7 @@ Section: x11
 Priority: optional
 Build-Depends: cmake,
                debhelper-compat (= 12),
+               libkf5windowsystem-dev,
                liblxqt0-dev (>= 0.15.0),
                libqt5x11extras5-dev,
                libxrender-dev,