changed return types to string to match parent methods

Author: Smef

src/Database/Query/FMBaseBuilder.php

@@ -1078,14 +1078,14 @@ public function getCountForPagination($columns = ['*'])
         return $this->count($columns);
     }
 
-    public function toRawSql()
+    public function toRawSql(): string
     {
         $this->computeWhereIns();
 
-        return $this->wheres;
+        return json_encode($this->wheres);
     }
 
-    public function toSql()
+    public function toSql(): string
     {
 
         return $this->toRawSql();