Rename model.php to Model.php

PSR-4: The terminating class name corresponds to a file name ending in .php. The file name MUST match the case of the terminating class name.
The subdirectory name * MUST match the case* of the sub-namespace names.
PSR-4 spec namespace \<NamespaceName>(\<SubNamespaceNames>)*\<ClassName>
Merge pull request #36 from sim2github/CaseFix

Case fix