upgrade gradle to 5.6.1
upgrade gradle to 5.6.1

This is a patch to Version 5.6,
see https://docs.gradle.org/5.6.1/release-notes.html#fixed-issues

auricgoldfinger/cgeo,S-Bartfast/cgeo,tobiasge/cgeo,auricgoldfinger/cgeo,cgeo/cgeo,cgeo/cgeo,rsudev/c-geo-opensource,matej116/cgeo,cgeo/cgeo,tobiasge/cgeo,rsudev/c-geo-opensource,S-Bartfast/cgeo,tobiasge/cgeo,rsudev/c-geo-opensource,cgeo/cgeo,matej116/cgeo,S-Bartfast/cgeo,matej116/cgeo,auricgoldfinger/cgeo