CMake 2.8.3 does not support CONFIG, use NO_MODULE instead

As discussed in https://github.com/ethz-asl/gtsam_catkin/issues/13

```
cmake_minimum_required(VERSION 2.8.3)
```
2.8.3 does not support CONFIG; use the backward compatible NO_MODULE instead

"The CONFIG option may be used to skip Module mode explicitly and switch to Config mode. It is synonymous to using NO_MODULE. " (http://www.cmake.org/cmake/help/v3.0/command/find_package.html)