pip(deps): update uvicorn requirement in /backend (#94)

Updates the requirements on [uvicorn](https://github.com/encode/uvicorn) to permit the latest version.
- [Release notes](https://github.com/encode/uvicorn/releases)
- [Changelog](https://github.com/encode/uvicorn/blob/master/docs/release-notes.md)
- [Commits](Kludex/uvicorn@0.27.0...0.34.1)

---
updated-dependencies:
- dependency-name: uvicorn
  dependency-version: 0.34.1
  dependency-type: direct:production
...

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

Author: dependabot[bot]

backend/requirements.txt

@@ -23,4 +23,4 @@ opencensus-ext-stackdriver==0.8.0
 opencensus==0.11.4
 
 # Server
-uvicorn==0.27.*
+uvicorn==0.34.*