move games/ski to python3

According to NEWS, games/ski was ported to python3 as of version 6.10.

Diff below updates to latest version and moves the port over to python3.

ok?

Index: Makefile
===================================================================
RCS file: /cvs/ports/games/ski/Makefile,v
retrieving revision 1.16
diff -u -p -u -r1.16 Makefile
--- Makefile 23 Feb 2021 19:39:23 -0000 1.16
+++ Makefile 28 Feb 2021 05:56:59 -0000
@@ -2,7 +2,8 @@

COMMENT= skiing simulation game

-DISTNAME= ski-6.11
+DISTNAME= ski-6.13
+
CATEGORIES= games

HOMEPAGE= http://catb.org/~esr/ski/
@@ -14,7 +15,6 @@ MAINTAINER= Gleydson Soares <gsoares@op
PERMIT_PACKAGE= Yes

MODULES= lang/python
-MODPY_VERSION = ${MODPY_DEFAULT_VERSION_2}

MODPY_ADJ_FILES= ski

Index: distinfo
===================================================================
RCS file: /cvs/ports/games/ski/distinfo,v
retrieving revision 1.5
diff -u -p -u -r1.5 distinfo
--- distinfo 4 Jun 2016 03:57:20 -0000 1.5
+++ distinfo 28 Feb 2021 05:56:59 -0000
@@ -1,2 +1,2 @@
-SHA256 (ski-6.11.tar.gz) = jdAzXQk7Og9EhqvSafK94wDZfSly7xRn/W3/XemjGyY=
-SIZE (ski-6.11.tar.gz) = 17740
+SHA256 (ski-6.13.tar.gz) = NOlVR+z+ezeR3wqB/vmvQi7Oz0mxqh6Tu7G6BnzNyVU=
+SIZE (ski-6.13.tar.gz) = 17808