## Python, ​<s> 44 </s>​ ​42 bytes

<!-- language: lang-py -->

    lambda s:s[:-1]+"\/ /\."[-ord(s[-1])&3::3]

Replaces the last character with the correspond set of two characters. [ideone link](http://ideone.com/IPVvuI)

*(-2 bytes thanks to @xsot's shorter mapping function)*