Updating docs to say that go1.8 is required

Author: benjih

docs/pages/contributing.rst

@@ -16,7 +16,7 @@ Learn more about the `forking workflow here <https://www.atlassian.com/git/tutor
 Building, running & testing
 ---------------------------
 
-You will need `Go 1.7 <https://golang.org>`_ . Instructions on how to set up your Go environment can be `found here <https://golang.org/doc/install>`_.   
+You will need `Go 1.8 <https://golang.org>`_ . Instructions on how to set up your Go environment can be `found here <https://golang.org/doc/install>`_.   
 
 .. code:: bash