Add missing scroll-snap-type values

Author: abaracedo

grammars/css.cson

@@ -1403,7 +1403,7 @@
           |text|text-after-edge|text-before-edge|text-bottom|text-top|thick|thin|titling-caps|top|top-outside|touch|traditional|transparent|triangle
           |ultra-condensed|ultra-expanded|under|underline|unicase|unset|upleft|uppercase|upright|use-glyph-orientation|use-script|verso|vertical
           |vertical-ideographic|vertical-lr|vertical-rl|vertical-text|view-box|visible|visibleFill|visiblePainted|visibleStroke|w-resize|wait|wavy
-          |weight|whitespace|wider|words|wrap|wrap-reverse|x-large|x-small|xx-large|xx-small|zero|zoom-in|zoom-out)
+          |weight|whitespace|wider|words|wrap|wrap-reverse|x|x-large|x-small|xx-large|xx-small|y|zero|zoom-in|zoom-out)
           (?![\\w-])
         '''
         'name': 'support.constant.property-value.css'