Add ! as in tests

Author: changfenxia

README.md

@@ -21,12 +21,12 @@ parameters and should return the string `"Happy holidays!"`.
 
 2. Write a function named `happyHolidaysTo`. This function should accept a
 parameter of the name of the person you want to wish happy holidays, and return
-the string `"Happy Holidays, ${name}"`
+the string `"Happy holidays, ${name}!"`
 
 3. Write a function named `happyHolidayTo`. This function should accept two
 parameters, the holiday you want to wish them well for, and the name of the
 person you're wishing well. This function should return the string
-`"Happy ${holiday}, ${name}"`
+`"Happy ${holiday}, ${name}!"`
 
 4. Write a function named `holidayCountdown`. This function should accept two
 parameters, the holiday name and number of days till that holiday. The function