Fix documentation build

The reference in contributing.rst was pointing to the wrong directory.

Change-Id: I41194f5c0483e6a6379e12b5d7137308397f1e13
diff --git a/doc/source/contributing.rst b/doc/source/contributing.rst
index 2aa0707..1728a61 100644
--- a/doc/source/contributing.rst
+++ b/doc/source/contributing.rst
@@ -1,4 +1,4 @@
 ============
 Contributing
 ============
-.. include:: ../../../CONTRIBUTING.rst
+.. include:: ../../CONTRIBUTING.rst