input: Write a python function to merge two strings.
  assert mergeStrings('Hello', 'World') == 'HelloWorld'
  assert mergeStrings('Good', 'Morning') == 'GoodMorning'
  assert mergeStrings('Python', 'Programming') == 'PythonProgramming'
output: def mergeStrings(str1, str2):
      return str1 + str2