Fix typo in configure command line option documentation

--enable-osu-*--sky130 should be --enable-osu-*-sky130

sky130/README

diff --git a/sky130/README b/sky130/README
index 6c40c67..6839a81 100644
--- a/sky130/README
+++ b/sky130/README
@@ -213,15 +213,15 @@
 		This 3rd party library is a set of open-source digital
 		standard cells.
 
-	--enable-osu-t12--sky130[=<path>]
+	--enable-osu-t12-sky130[=<path>]
 		This 3rd party library is a set of open-source digital
 		standard cells at 12 track pitch height.
 
-	--enable-osu-t15--sky130[=<path>]
+	--enable-osu-t15-sky130[=<path>]
 		This 3rd party library is a set of open-source digital
 		standard cells at 15 track pitch height.
 
-	--enable-osu-t18--sky130[=<path>]
+	--enable-osu-t18-sky130[=<path>]
 		This 3rd party library is a set of open-source digital
 		standard cells at 18 track pitch height.