Doc: corrected punctuation (,)

Change-Id: Id1b7bf4c6ff1fa7286cafdc5ffe7cdab636a622b
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Reviewed-by: Martin Smith <martin.smith@digia.com>

src/controls/ToolBar.qml

@@ -52,7 +52,7 @@ import QtQuick.Controls.Private 1.0
     provides styling and is generally designed to work well with ToolButton as
     well as other controls.
 
-    Note that the ToolBar does not provide a layout of its own but requires you
+    Note that the ToolBar does not provide a layout of its own, but requires you
     to position its contents, for instance by creating a Row.
 
     \code