Bump docutils from 0.15.2 to 0.16

Bumps [docutils](http://docutils.sourceforge.net/) from 0.15.2 to 0.16.

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

requirements.txt

@@ -4,7 +4,7 @@ azure-mgmt-dns==3.0.0
 boto3==1.11.0
 botocore==1.14.0
 dnspython==1.16.0
-docutils==0.15.2
+docutils==0.16
 dyn==1.8.1
 edgegrid-python==1.1.1
 futures==3.2.0; python_version < '3.0'