Merge pull request #5255 from xamarin/bump-master-version

Post branch version number bump

Make.versions

@@ -43,5 +43,5 @@
 #   line changed in git).
 #
 
-IOS_PACKAGE_VERSION=12.5.1.$(IOS_COMMIT_DISTANCE)
-MAC_PACKAGE_VERSION=5.5.1.$(MAC_COMMIT_DISTANCE)
+IOS_PACKAGE_VERSION=12.6.0.$(IOS_COMMIT_DISTANCE)
+MAC_PACKAGE_VERSION=5.6.0.$(MAC_COMMIT_DISTANCE)