Fix doc build warnings

Fix warnings:
doc/image-building.rst:415:undefined label: deploy_a_registry
(if the link has no caption the label must precede a section header)

Change-Id: I8d921f3b05acf9304ccf41e172926887088b97d7

1 files changed, 1 insertions, 0 deletions

diff --git a/tox.ini b/tox.ini
index 8ec8962d8..bcbd332fd 100644
--- a/tox.ini
+++ b/tox.ini
@@ -46,6 +46,7 @@ commands = {posargs}
 
 [testenv:docs]
 commands =
+  rm -rf doc/build
   doc8 doc
   python setup.py build_sphinx