input: Write a python function to check if one string is a rotation of another.
  assert isRotation('abc', 'cab') == True
  assert isRotation('hello', 'lohel') == True
  assert isRotation('waterbottle', 'erbottlewat') == True
  assert isRotation('abcd', 'dabc') == True
  assert isRotation('abc', 'def') == False
output: def isRotation(s1, s2):
      if len(s1) != len(s2):
          return False
      return s2 in s1 + s1