fix typo to make doctests passs

README.md

@@ -695,7 +695,7 @@ If you have an IntervalDict, and you want to iterate over its atomic intervals i
 >>> d[P.open(1, 2)] = 'peach stone'
 >>> in_order = sorted([(atomic, value) for key, value in d.items() for atomic in key])
 >>> in_order  # a list of 3 items
-[((0,1), 'peach'), ((1,2), 'peach stone'), ((2,3), 'peach'))]
+[((0,1), 'peach'), ((1,2), 'peach stone'), ((2,3), 'peach')]
 
 ```