Bump attrs from 19.1.0 to 19.3.0 in /packages/service-library (#1330)

Bumps [attrs](https://github.com/python-attrs/attrs) from 19.1.0 to 19.3.0.
- [Release notes](https://github.com/python-attrs/attrs/releases)
- [Changelog](https://github.com/python-attrs/attrs/blob/master/CHANGELOG.rst)
- [Commits](python-attrs/attrs@19.1.0...19.3.0)

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

Co-authored-by: Pedro Crespo <[email protected]>

Author: dependabot-preview[bot]

packages/service-library/requirements/_base.txt

@@ -8,7 +8,7 @@ aiohttp==3.6.2            # via -r requirements/_base.in (line 10), aiozipkin
 aiopg[sa]==1.0.0          # via -r requirements/_base.in (line 11)
 aiozipkin==0.6.0          # via -r requirements/_base.in (line 12)
 async-timeout==3.0.1      # via aiohttp
-attrs==19.1.0             # via -r requirements/_base.in (line 19), aiohttp, jsonschema, openapi-core
+attrs==19.3.0             # via -r requirements/_base.in (line 19), aiohttp, jsonschema, openapi-core
 chardet==3.0.4            # via aiohttp
 idna==2.8                 # via yarl
 isodate==0.6.0            # via openapi-core

packages/service-library/requirements/_test.txt

@@ -9,7 +9,7 @@ aiopg[sa]==1.0.0          # via -r requirements/_base.txt (line 8)
 aiozipkin==0.6.0          # via -r requirements/_base.txt (line 9)
 astroid==2.3.3            # via pylint
 async-timeout==3.0.1      # via -r requirements/_base.txt (line 10), aiohttp
-attrs==19.1.0             # via -r requirements/_base.txt (line 11), aiohttp, jsonschema, openapi-core, pytest, pytest-docker
+attrs==19.3.0             # via -r requirements/_base.txt (line 11), aiohttp, jsonschema, openapi-core, pytest, pytest-docker
 certifi==2019.11.28       # via requests
 chardet==3.0.4            # via -r requirements/_base.txt (line 12), aiohttp, requests
 coverage==4.5.1           # via -r requirements/_test.in (line 9), coveralls, pytest-cov