Mk/Uses/tcl.mk: Fix typo

[00:00:01] Gathering ports metadata
[00:00:11] Warning: (graphics/py-pillow): make: "/usr/ports/Mk/Uses/tcl.mk" line 168: Unknown modifier "s/9/9./"
[00:00:11] Warning: (graphics/py-pillow): make: "/usr/ports/Mk/Uses/tcl.mk" line 168: Undefined variable "${_TCLTK_WANTED_VERSION:S/8/8./:s/9/9./}"
[00:00:11] Warning: (graphics/py-pillow): make: Fatal errors encountered -- cannot continue
[00:00:11] Warning: (graphics/py-pillow): Error: Error looking up dependencies for graphics/py-pillow
[00:00:12] Error: /usr/local/share/poudriere/bulk.sh:gather_port_vars:183:Fatal errors encountered gathering ports metadata

Approved by: portmgr (blanket)