Fix cachekey issue (#471)

This should fix #470 by making sure all columns are strings before imploding them.

Signed-off-by: James Cole <[email protected]>

Author: JC5

src/CacheKey.php

@@ -263,6 +263,10 @@ protected function getQueryColumns(array $columns) : string
             return "_" . implode("_", $columns);
         }
 
+        $columns = array_map(function ($column) {
+            return $this->expressionToString($column);
+        }, $columns);
+        
         return "_" . implode("_", $columns);
     }