Fix aiohttp importing for Windows

[bojiang]

Description

Todo: enable integration tests for the development server on Windows(#1546) to avoid breaks in the future.

Motivation and Context

How Has This Been Tested?

Types of changes

• Breaking change (fix or feature that would cause existing functionality to change)
• New feature and improvements (non-breaking change which adds/improves functionality)
• Bug fix (non-breaking change which fixes an issue)
• Code Refactoring (internal change which is not user facing)
• Documentation
• Test, CI, or build

Component(s) if applicable

• BentoService (service definition, dependency management, API input/output adapters)
• Model Artifact (model serialization, multi-framework support)
• Model Server (mico-batching, dockerisation, logging, OpenAPI, instruments)
• YataiService gRPC server (model registry, cloud deployment automation)
• YataiService web server (nodejs HTTP server and web UI)
• Internal (BentoML's own configuration, logging, utility, exception handling)
• BentoML CLI

Checklist:

• My code follows the bentoml code style, both ./dev/format.sh and
  ./dev/lint.sh script have passed
  (instructions).
• My change reduces project test coverage and requires unit tests to be added
• I have added unit tests covering my code change
• My change requires a change to the documentation
• I have updated the documentation accordingly

[codecov]

Codecov Report

Merging #1557 (58ae641) into master (ebe69b0) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1557      +/-   ##
==========================================
- Coverage   69.14%   69.13%   -0.02%     
==========================================
  Files         152      152              
  Lines       10188    10189       +1     
==========================================
- Hits         7045     7044       -1     
- Misses       3143     3145       +2     

Impacted Files	Coverage Δ
bentoml/marshal/marshal.py	72.51% <100.00%> (-1.02%)	⬇️

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[bnapora]

Great. Will 0.12.1 be available on pypi or just from source?

[parano]

@bnapora it will be released on PyPI soon, you may watch the repo to subscribe to new release notifications