fix: compiling the hashmap example

tested with ghc 7.4.1

I am not sure importing the submodule Types from karver is the right thing to do, but however the example does not compile.
cabal reports that karver is correctly installed : 
$ cabal list karver
* karver
    Synopsis: A simple template engine, inspired by jinja2
    Default available version: 0.1.0
    Installed versions: 0.1.0
    License:  BSD3


regards,