Fix copy-paste error

CMakeLists.txt

@@ -47,7 +47,11 @@ find_package(KF5Akonadi ${AKONADI_VERSION} CONFIG REQUIRED)
 
 set(Prison_MIN_VERSION "1.2.2")
 find_package(KF5Prison ${Prison_MIN_VERSION})
-set_package_properties(Prison PROPERTIES DESCRIPTION "Prison" URL "http://projects.kde.org/prison" TYPE OPTIONAL$
+set_package_properties(Prison PROPERTIES
+                       DESCRIPTION "Prison"
+                       URL "http://projects.kde.org/prison"
+                       TYPE OPTIONAL
+                       PURPOSE "Needed to show mobile barcodes of your contacts")
 if (KF5Prison_FOUND)
     add_definitions(-DHAVE_PRISON)
 endif()