Fix _unchecked session removal for arrays

Using triple `=== ['_unchecked']` can never return `true`

lib/session.js

@@ -59,7 +59,7 @@ function storeData (input, data) {
     let val = input[i]
 
     // Delete values when users unselect checkboxes
-    if (val === '_unchecked' || val === ['_unchecked']) {
+    if (val === '_unchecked') {
       delete data[i]
       continue
     }