Fix some minor rubocop (lint) offenses

unipoly-mlmmj-ldap-sync

@@ -27,7 +27,8 @@ def connect_ldap
     }
   )
 
-  ldap_addr = "#{@configuration['ldap']['host']}:#{@configuration['ldap']['port']}"
+  ldap_addr = @configuration['ldap']['host'] + ':' +
+              @configuration['ldap']['port']
   begin
     if conn.bind
       conn
@@ -142,7 +143,7 @@ end
 def main
   # Parse configuration, bind to LDAP server
   @configuration = read_configuration(@configuration_file)
-  conn = connect_ldap()
+  conn = connect_ldap
 
   domain = @configuration['domain']
   basetree = @configuration['ldap']['lists']['basetree']