Merge pull request #9 from sergoslav/hotfix/query-operator-case-insensitive

query operator as lowercase to escape casesensetive troubles.

Author: pdphilip

src/DSL/QueryBuilder.php

@@ -279,7 +279,7 @@ private function _parseCondition($condition, $parentField = null): array
 
             return ['match' => [$field => $value]];
         } else {
-            $operator = key($value);
+            $operator = strtolower(key($value));
             $operand = current($value);
             $queryPart = [];