identifier keyword to beginPath

mathGlyph -> PointToSegmentPen -> drawPoints -> pointPen -> beginPath
gets an ‘identifier’ argument from the ufo3 drawPoints. Which trips an
error. This alleviates the problem but does not address anything that
beginPath should be doing with the identifier.

Lib/robofab/pens/pointPen.py

@@ -17,7 +17,7 @@ class BasePointToSegmentPen(AbstractPointPen):
 	def __init__(self):
 		self.currentPath = None
 
-	def beginPath(self):
+	def beginPath(self, **kwargs):
 		assert self.currentPath is None
 		self.currentPath = []