python3.8: fix DeprecationWarning in qt/paytoedit

.../electrum/electrum/gui/qt/paytoedit.py:221: DeprecationWarning: an integer is required (got type float).  Implicit conversion to integers using __int__ is deprecated, and may be removed in a future version of Python.
  self.setMinimumHeight(h)

electrum/gui/qt/paytoedit.py

@@ -216,7 +216,7 @@ def paytomany(self):
     def update_size(self):
         lineHeight = QFontMetrics(self.document().defaultFont()).height()
         docHeight = self.document().size().height()
-        h = docHeight * lineHeight + 11
+        h = round(docHeight * lineHeight + 11)
         h = min(max(h, self.heightMin), self.heightMax)
         self.setMinimumHeight(h)
         self.setMaximumHeight(h)