Require at least Redmine 5.1

Author: dkastl

init.rb

@@ -8,7 +8,7 @@
   description 'Adds location-based task management and maps'
   version '6.0.0'
 
-  requires_redmine :version_or_higher => '5.0.0'
+  requires_redmine :version_or_higher => '5.1.0'
 
   project_module :gtt do
     permission :manage_gtt_settings, {