CSS column-count property is unitless

src/dom/CSSProperty.js

@@ -22,6 +22,7 @@
  * CSS properties which accept numbers but are not in units of "px".
  */
 var isUnitlessNumber = {
+  columnCount: true,
   fillOpacity: true,
   flex: true,
   flexGrow: true,

src/dom/__tests__/CSSPropertyOperations-test.js

@@ -70,6 +70,7 @@ describe('CSSPropertyOperations', function() {
 
   it('should not append `px` to styles that might need a number', function() {
     var unitlessProperties = [
+      'columnCount',
       'fillOpacity',
       'flex',
       'flexGrow',