Bump boto3 from 1.16.47 to 1.16.51

Bumps [boto3](https://github.com/boto/boto3) from 1.16.47 to 1.16.51.
- [Release notes](https://github.com/boto/boto3/releases)
- [Changelog](https://github.com/boto/boto3/blob/develop/CHANGELOG.rst)
- [Commits](boto/boto3@1.16.47...1.16.51)

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

requirements.txt

@@ -1,5 +1,5 @@
 asn1crypto==1.4.0
-boto3==1.16.47
+boto3==1.16.51
 bcrypt==3.2.0
 certifi==2020.12.5
 cffi==1.14.4