upgrade roundcube to 1.6.1 (#3224)

install/upgrade/upgrade.conf

@@ -47,7 +47,7 @@ pma_v='5.2.0'
 
 # Set version of RoundCube (Webmail) to update during upgrade if not already installed
 # Note: only applies to "non-apt installs >= 1.4.0 or manually phased out"
-rc_v='1.6.0'
+rc_v='1.6.1'
 
 # Set version of Rainloop (Webmail) to update during upgrade if not already installed
 rl_v='1.17.0'