Relax botocore dependency specification

[jakob-keller]

Description of Change

This PR intends to improve general compatibility of aiobotocore within the Python ecosystem by relaxing the dependency specification of botocore, as well as boto3 and awscli.

Assumptions

Upstream diff contains no changes that require adjustments to the aiobotocore codebase.

Checklist for All Submissions

• I have added change info to CHANGES.rst
• If this is resolving an issue (needed so future developers can determine if change is still necessary and under what conditions) (can be provided via link to issue with these details):
  • Detailed description of issue
  • Alternative methods considered (if any)
  • How issue is being resolved
  • How issue can be reproduced
• If this is providing a new feature (can be provided via link to issue with these details):
  • Detailed description of new feature
  • Why needed
  • Alternatives methods considered (if any)

Checklist when updating botocore and/or aiohttp versions

• I have read and followed CONTRIBUTING.rst
• I have updated test_patches.py where/if appropriate (also check if no changes necessary)
• I have ensured that the awscli/boto3 versions match the updated botocore version

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.92%. Comparing base (ea04963) to head (aae1c3d).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1256      +/-   ##
==========================================
- Coverage   87.97%   87.92%   -0.06%     
==========================================
  Files          67       67              
  Lines        5904     5904              
==========================================
- Hits         5194     5191       -3     
- Misses        710      713       +3     

Flag	Coverage Δ
unittests	87.92% <ø> (-0.06%)	⬇️

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