CSS: Don't auto-append "px" to possibly-unitless CSS grid properties

This commit adds some CSS grid-related properties to jQuery.cssNumber.

Fixes jquerygh-4007

Author: enbo

src/css.js

@@ -194,6 +194,13 @@ jQuery.extend( {
 		"flexGrow": true,
 		"flexShrink": true,
 		"fontWeight": true,
+		"gridArea": true,
+		"gridColumn": true,
+		"gridColumnEnd": true,
+		"gridColumnStart": true,
+		"gridRow": true,
+		"gridRowEnd": true,
+		"gridRowStart": true,
 		"lineHeight": true,
 		"opacity": true,
 		"order": true,