fix rapid7#5074 - missing thread join

Author: medievia96

lib/msf/ui/console/command_dispatcher/core.rb

@@ -629,6 +629,8 @@ def cmd_connect(*args)
       n2c.kill
     end
 
+    c2n.join
+    n2c.join
 
     sock.close rescue nil
     infile.close if infile