input: Write a function to capitalize a character at a given position in a string.
  assert capitalizeCharacter("hello", 1) == "hEllo"
  assert capitalizeCharacter("python", 0) == "Python"
  assert capitalizeCharacter("capitalize", 4) == "capiTalize"
output: def capitalizeCharacter(s, pos):
      if pos < 0 or pos >= len(s):
          return s
      return s[:pos] + s[pos].upper() + s[pos+1:]