Bump httpx from 0.7.5 to 0.7.6 (#38)

Bumps [httpx](https://github.com/encode/httpx) from 0.7.5 to 0.7.6.
- [Release notes](https://github.com/encode/httpx/releases)
- [Changelog](https://github.com/encode/httpx/blob/master/CHANGELOG.md)
- [Commits](encode/httpx@0.7.5...0.7.6)

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

test-requirements.txt

@@ -22,7 +22,7 @@ h2==3.1.1                 # via httpx
 hpack==3.0.0              # via h2
 hstspreload==2019.8.27    # via httpx
 httptools==0.0.13         # via uvicorn
-httpx==0.7.5
+httpx==0.7.6
 hyperframe==5.2.0         # via h2
 idna==2.8                 # via httpx, requests, yarl
 importlib-metadata==0.19  # via pluggy, pytest