media-fonts/source-pro: depend on old freetype

This version includes an SVG table that causes
=media-libs/freetype-2.12.1 to be unable to calculate cell height,
resulting in unusable output with lines stacked on top of each other in
alacritty and probably other programs.

Bug: https://bugs.gentoo.org/865103
Signed-off-by: Ronny (tastytea) Gutbrod <gentoo@tastytea.de>

media-fonts/source-pro/source-pro-20170111.ebuild

@@ -28,6 +28,7 @@ RESTRICT="binchecks strip"
 RDEPEND="
 	media-libs/fontconfig
 	cjk? ( media-fonts/source-han-sans )
+	!>=media-libs/freetype-2.12.1
 "
 
 FONT_CONF=( "${FILESDIR}"/63-${PN}.conf )