pyupgrade --py37-plus **/*.py (#1654)

* pyupgrade --py37-plus **/*.py

* fixup! Format Python code with psf/black push

data_structures/stacks/stack.py

@@ -1,7 +1,7 @@
 __author__ = "Omkar Pathak"
 
 
-class Stack(object):
+class Stack:
     """ A stack is an abstract data type that serves as a collection of
     elements with two principal operations: push() and pop(). push() adds an
     element to the top of the stack, and pop() removes an element from the top