docs: Build more often. (#321)

The script will just die soon if another insance already runs (it uses
a file lock), so there's no fear at starting it too often.

Also the script does no longer build documentation that has not
changed (by checking the cpython and translation shas), so runnig the
script more often will not introduce more load, just faster builds.

salt/docs/init.sls

@@ -78,7 +78,6 @@ docsbuild-full:
     - name: /srv/docsbuild/venv/bin/python /srv/docsbuild/scripts/build_docs.py
     - user: docsbuild
     - minute: 7
-    - hour: 0
     - require:
       - cmd: virtualenv-dependencies