fix dependency lookup

the target is called ConfigCore, the relevant cmake config is not.
notably KF5ConfigConfig.cmake is the present file, so look for the
correct name, otherwise the dependency isn't found

src/libkwineffects/KWinEffectsConfig.cmake.in

@@ -3,7 +3,7 @@
 include(CMakeFindDependencyMacro)
 find_dependency(Qt5Core "@QT_MIN_VERSION@")
 find_dependency(Qt5Gui "@QT_MIN_VERSION@")
-find_dependency(KF5ConfigCore "@KF5_MIN_VERSION@")
+find_dependency(KF5Config "@KF5_MIN_VERSION@")
 find_dependency(KF5CoreAddons "@KF5_MIN_VERSION@")
 find_dependency(KF5WindowSystem "@KF5_MIN_VERSION@")