Bump aiosignal from 1.1.2 to 1.2.0 (#110)

Bumps [aiosignal](https://github.com/aio-libs/aiosignal) from 1.1.2 to 1.2.0.
- [Release notes](https://github.com/aio-libs/aiosignal/releases)
- [Changelog](https://github.com/aio-libs/aiosignal/blob/master/CHANGES.rst)
- [Commits](aio-libs/aiosignal@v1.1.2...v1.2.0)

---
updated-dependencies:
- dependency-name: aiosignal
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements/dev.txt

@@ -8,7 +8,7 @@ aiodns==3.0.0 ; sys_platform == "linux" or sys_platform == "darwin" and python_v
     # via -r requirements/base.txt
 aiohttp-theme==0.1.6
     # via -r requirements/doc.txt
-aiosignal==1.1.2
+aiosignal==1.2.0
     # via -r requirements/base.txt
 alabaster==0.7.12
     # via sphinx