Update standard to c++20

Author: AdrianTM

mx-packageinstaller.pro

@@ -22,7 +22,7 @@
 # **********************************************************************/
 
 QT       += core gui xml network widgets
-CONFIG   += debug_and_release warn_on strict_c++ c++17
+CONFIG   += debug_and_release warn_on strict_c++ c++20
 
 CONFIG(release, debug|release) {
     DEFINES += NDEBUG