fix setFetchMode() signature inconsistencies

lib/Doctrine/DBAL/Driver/IBMDB2/DB2Statement.php

@@ -148,7 +148,7 @@ class DB2Statement implements \IteratorAggregate, Statement
     /**
      * {@inheritdoc}
      */
-    public function setFetchMode($fetchStyle = \PDO::FETCH_BOTH, $arg2 = null, $arg3 = null)
+    public function setFetchMode($fetchStyle, $arg2 = null, $arg3 = null)
     {
         $this->_defaultFetchStyle = $fetchStyle;
     }

lib/Doctrine/DBAL/Driver/Mysqli/MysqliStatement.php

@@ -326,7 +326,7 @@ class MysqliStatement implements \IteratorAggregate, Statement
     /**
      * {@inheritdoc}
      */
-    public function setFetchMode($fetchMode = PDO::FETCH_BOTH, $arg2 = null, $arg3 = null)
+    public function setFetchMode($fetchMode, $arg2 = null, $arg3 = null)
     {
         $this->_defaultFetchStyle = $fetchMode;
     }

lib/Doctrine/DBAL/Driver/OCI8/OCI8Statement.php

@@ -190,7 +190,7 @@ class OCI8Statement implements \IteratorAggregate, Statement
     /**
      * {@inheritdoc}
      */
-    public function setFetchMode($fetchStyle = PDO::FETCH_BOTH, $arg2 = null, $arg3 = null)
+    public function setFetchMode($fetchStyle, $arg2 = null, $arg3 = null)
     {
         $this->_defaultFetchStyle = $fetchStyle;
     }

lib/Doctrine/DBAL/Driver/SQLSrv/SQLSrvStatement.php

@@ -175,7 +175,7 @@ class SQLSrvStatement implements IteratorAggregate, Statement
         }
     }
 
-    public function setFetchMode($fetchStyle = PDO::FETCH_BOTH, $arg2 = null, $arg3 = null)
+    public function setFetchMode($fetchStyle, $arg2 = null, $arg3 = null)
     {
         $this->defaultFetchStyle = $fetchStyle;
     }