[style] Change private slant tag

https://github.com/harfbuzz/harfbuzz/issues/3200#issuecomment-918352162
diff --git a/src/hb-style.h b/src/hb-style.h
index 54a3b59..352f565 100644
--- a/src/hb-style.h
+++ b/src/hb-style.h
@@ -62,7 +62,7 @@
   HB_STYLE_TAG_ITALIC		= HB_TAG ('i','t','a','l'),
   HB_STYLE_TAG_OPTICAL_SIZE	= HB_TAG ('o','p','s','z'),
   HB_STYLE_TAG_SLANT_ANGLE	= HB_TAG ('s','l','n','t'),
-  HB_STYLE_TAG_SLANT_RATIO	= HB_TAG ('s','l','n','T'),
+  HB_STYLE_TAG_SLANT_RATIO	= HB_TAG ('S','l','n','t'),
   HB_STYLE_TAG_WIDTH		= HB_TAG ('w','d','t','h'),
   HB_STYLE_TAG_WEIGHT		= HB_TAG ('w','g','h','t'),