1) in ocaml language

Write a function that takes a, b, and c and
return a string of the tree values in sorted order.
You might want to write a function combine a b c
that returns a contact ":" b contact ":" contact c.
You will use string_of_int function to convert int
to string.

sort_as_str 5 4 6;; return "4:5:6"
sort_as_str 4 6 5;; return "4:5:6"
sort_as_str 4 5 6;; return "4:5"6"