Update LXQt build dependencies.

debian/changelog

@@ -2,6 +2,7 @@ lxqt-sudo (0.15.0-0ubuntu1) UNRELEASED; urgency=medium
 
   * New upstream release.
     - Update upstream signing key.
+    - Update LXQt build dependencies.
   * Update Standards-version to 4.5.0, no changes needed.
 
  -- Simon Quigley <tsimonq2@ubuntu.com>  Thu, 30 Apr 2020 23:43:45 -0500

debian/control

@@ -6,7 +6,7 @@ Section: x11
 Priority: optional
 Build-Depends: debhelper (>= 12),
                libkf5windowsystem-dev,
-               liblxqt0-dev (>= 0.14.0),
+               liblxqt0-dev (>= 0.15.0),
                libqt5svg5-dev,
                libqt5x11extras5-dev,
                libx11-dev