Bump sqlalchemy from 1.3.7 to 1.3.8

Bumps [sqlalchemy](https://github.com/sqlalchemy/sqlalchemy) from 1.3.7 to 1.3.8.
- [Release notes](https://github.com/sqlalchemy/sqlalchemy/releases)
- [Changelog](https://github.com/sqlalchemy/sqlalchemy/blob/master/CHANGES)
- [Commits](https://github.com/sqlalchemy/sqlalchemy/commits)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

requirements-dev.txt

@@ -13,7 +13,7 @@ pytest-cov==2.7.1
 pytest-sugar==0.9.2
 pytest==5.1.1
 python-dateutil==2.8.0
-sqlalchemy==1.3.7
+sqlalchemy==1.3.8
 trafaret==1.2.0
 pymysql==0.9.3
 -r requirements-doc.txt