Bump KF5 required version to 5.42

This is needed by
Differential Revision: https://phabricator.kde.org/D9180
where KPackage::fileUrl is used.

CMakeLists.txt

@@ -4,7 +4,7 @@ set(PROJECT_VERSION_MAJOR 5)
 cmake_minimum_required(VERSION 2.8.12 FATAL_ERROR)
 
 set(QT_MIN_VERSION "5.4.0")
-set(KF5_MIN_VERSION "5.15.0")
+set(KF5_MIN_VERSION "5.42.0")
 find_package(Qt5 ${QT_MIN_VERSION} CONFIG REQUIRED COMPONENTS Widgets Quick QuickWidgets Test)
 find_package(ECM 1.8.0 REQUIRED NO_MODULE)
 set(CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake ${ECM_MODULE_PATH} ${ECM_KDE_MODULE_DIR})