Downgrade Coverage to 4.5.4

[chanchiem]

Coverage 5.0 had introduced a bug for us and is causing our tox tests to throw a
Segment Missing Exception upon starting coverage. Downgrading to 4.5.4 while we
investigate the root cause.

Issue #, if available:
#195

Description of changes:
Downgraded coverage to 4.5.4

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-io]

Codecov Report

Merging #197 into master will increase coverage by 2.25%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #197      +/-   ##
==========================================
+ Coverage   81.58%   83.84%   +2.25%     
==========================================
  Files          72       77       +5     
  Lines        2743     3003     +260     
==========================================
+ Hits         2238     2518     +280     
+ Misses        505      485      -20

Impacted Files	Coverage Δ
aws_xray_sdk/core/models/trace_header.py	100% <0%> (ø)	⬆️
aws_xray_sdk/core/sampling/rule_cache.py	100% <0%> (ø)	⬆️
aws_xray_sdk/core/async_recorder.py	92% <0%> (ø)
aws_xray_sdk/ext/aiohttp/middleware.py	97.72% <0%> (ø)
aws_xray_sdk/ext/aiohttp/client.py	97.5% <0%> (ø)
aws_xray_sdk/ext/pymongo/patch.py	0% <0%> (ø)
aws_xray_sdk/ext/aiobotocore/patch.py	92.85% <0%> (ø)
aws_xray_sdk/core/models/subsegment.py	96.96% <0%> (+0.09%)	⬆️
aws_xray_sdk/core/daemon_config.py	97.95% <0%> (+0.18%)	⬆️
aws_xray_sdk/core/streaming/default_streaming.py	96.77% <0%> (+0.22%)	⬆️
... and 21 more

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