QmlDesigner: Support QtQuick 2.7

Qt 5.7 comes with QtQuick 2.7, and Qt 5.7 will most likely come
with Qt Creator 4.0.x

Change-Id: I3425ee59adde61d5e15f39c81bc10ab286d9f80a
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@theqtcompany.com>

src/plugins/qmldesigner/designercore/model/texttomodelmerger.cpp

@@ -69,7 +69,7 @@ static inline QStringList supportedVersionsList()
         QStringLiteral("2.0"), QStringLiteral("2.1"),
         QStringLiteral("2.2"), QStringLiteral("2.3"),
         QStringLiteral("2.4"), QStringLiteral("2.5"),
-        QStringLiteral("2.6")
+        QStringLiteral("2.6"), QStringLiteral("2.7")
     };
     return list;
 }