Bump botocore from 1.20.7 to 1.20.15

Bumps [botocore](https://github.com/boto/botocore) from 1.20.7 to 1.20.15.
- [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/1.20.7...1.20.15)

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

requirements-docs.txt

@@ -58,7 +58,7 @@ boto==2.49.0
     # via
     #   -r requirements-tests.txt
     #   moto
-botocore==1.20.7
+botocore==1.20.15
     # via
     #   -r requirements-docs.in
     #   -r requirements-tests.txt

requirements-tests.txt

@@ -24,7 +24,7 @@ boto3==1.17.7
     #   moto
 boto==2.49.0
     # via moto
-botocore==1.20.7
+botocore==1.20.15
     # via
     #   aws-xray-sdk
     #   boto3

requirements.txt

@@ -33,7 +33,7 @@ blinker==1.4
     #   raven
 boto3==1.17.7
     # via -r requirements.in
-botocore==1.20.7
+botocore==1.20.15
     # via
     #   -r requirements.in
     #   boto3