Adjust sphinx apidoc import as for version 2.0 requires (#606)

Fix to make #605 work

Author: sliverc

docs/conf.py

@@ -27,7 +27,7 @@
 django.setup()
 
 # Auto-generate API documentation.
-from sphinx.apidoc import main
+from sphinx.ext.apidoc import main
 main(['sphinx-apidoc', '-e',  '-T',  '-M',  '-f',  '-o', 'apidoc', '../rest_framework_json_api'])
 
 # -- General configuration ------------------------------------------------