fix typo in comments
Merge pull request #62 from crigor/typo

fix typo in comments
Add support for Google Compute Engine

This commit is the result of collaboration among David McWherter, Anders
Ingemann, and me. The rename to build-debian-cloud is at Anders's
initiative.

David's and my work on this is Copyright 2013 Google, Inc. and is
released under the Apache License 2.0.