Add modulo

calculator/operators.py

 """
 Operator module contains the Operator class and a list of standard operators.
 """
+
+
 class Operator:
     """
     Operator class is a binary operator with a symbol, a precedence and an evaluation function.
@@ -21,6 +23,7 @@ class Operator:
 STANDARD_OPERATORS = {
     '+': Operator('+', 1, lambda a, b: a + b),
     '-': Operator('-', 1, lambda a, b: a - b),
-    '*': Operator('×', 2, lambda a, b: a * b),
+    '*': Operator('*', 2, lambda a, b: a * b),
     '/': Operator('/', 2, lambda a, b: a / b),
+    '%': Operator('%', 2, lambda a, b: a % b),
 }