Fix typo

app.py

@@ -25,7 +25,7 @@ def toss_a_die(k: int) -> int:
     Args:
         k: An integer specifying the number of sides on the die. If not specified, a good default would be to assume k=6 sides.
     """
-    if k=None: 
+    if k==None: 
         k=6
     value = 3
     return f"The random roll of a dice gives a value of {value}"