Fix injecting custom class names for vertical lines

Fixes injecting custom class names for vertical lines spanning over a period of time longer than day (eg. month)

Author: Rafał Zakrzewski

src/lib/columns/Columns.js

@@ -73,7 +73,7 @@ class Columns extends Component {
           (firstOfType ? ' rct-vl-first' : '') +
           (minUnit === 'day' || minUnit === 'hour' || minUnit === 'minute'
             ? ` rct-day-${time.day()} `
-            : '') +
+            : ' ') +
           classNamesForTime.join(' ')
 
         const left = getLeftOffsetFromDate(time.valueOf())
@@ -112,4 +112,4 @@ ColumnsWrapper.defaultProps = {
   ...passThroughPropTypes
 }
 
-export default ColumnsWrapper
+export default ColumnsWrapper