ship: repair hydrostatics-plotting for py2

src/Mod/Ship/shipHydrostatics/TaskPanel.py

@@ -30,7 +30,7 @@ import Part
 from FreeCAD import Units
 from PySide import QtGui, QtCore
 from . import PlotAux
-from . import Instance
+import Instance
 from shipUtils import Paths
 import shipUtils.Units as USys
 import shipUtils.Locale as Locale