Bump botocore from 1.15.5 to 1.15.11

Bumps [botocore](https://github.com/boto/botocore) from 1.15.5 to 1.15.11.
- [Release notes](https://github.com/boto/botocore/releases)
- [Changelog](https://github.com/boto/botocore/blob/develop/CHANGELOG.rst)
- [Commits](https://github.com/boto/botocore/compare/1.15.5...1.15.11)

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

requirements.txt

@@ -2,7 +2,7 @@ PyYaml==5.3
 azure-common==1.1.24
 azure-mgmt-dns==3.0.0
 boto3==1.12.11
-botocore==1.15.5
+botocore==1.15.11
 dnspython==1.16.0
 docutils==0.16
 dyn==1.8.1