[AIRFLOW-6667] Bump copy-webpack-plugin to resolve serialize-javascript advisory

[ryw]

Bump copy-webpack-plugin to resolve serialize-javascript advisory
https://npmjs.com/advisories/1426

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Issue link: AIRFLOW-6667

Make sure to mark the boxes below before creating PR: [x]

• Description above provides context of the change
• Commit message/PR title starts with [AIRFLOW-NNNN]. AIRFLOW-NNNN = JIRA ID^*
• Unit tests coverage for changes (not needed for documentation changes)
• Commits follow "How to write a good git commit message"
• Relevant documentation is updated including usage instructions.
• I will engage committers as explained in Contribution Workflow Example.

^* For document-only changes commit message can start with [AIRFLOW-XXXX].

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In case of fundamental code change, Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in UPDATING.md.
Read the Pull Request Guidelines for more information.

[codecov-io]

Codecov Report

Merging #7282 into master will decrease coverage by 0.87%.
The diff coverage is 86.22%.

@@            Coverage Diff             @@
##           master    #7282      +/-   ##
==========================================
- Coverage   85.45%   84.58%   -0.88%     
==========================================
  Files         841      864      +23     
  Lines       40363    40455      +92     
==========================================
- Hits        34491    34217     -274     
- Misses       5872     6238     +366

Impacted Files	Coverage Δ
airflow/operators/s3_to_hive_operator.py	0% <0%> (-93.97%)	⬇️
airflow/operators/mysql_to_hive.py	0% <0%> (-100%)	⬇️
...w/providers/apache/hive/operators/mysql_to_hive.py	0% <0%> (ø)
...flow/contrib/example_dags/example_gcs_to_gdrive.py	100% <100%> (ø)	⬆️
.../amazon/aws/operators/google_api_to_s3_transfer.py	100% <100%> (ø)
...rflow/providers/amazon/aws/operators/sftp_to_s3.py	100% <100%> (ø)
...s/google/suite/operators/gcs_to_gdrive_operator.py	100% <100%> (ø)
airflow/contrib/operators/mongo_to_s3.py	100% <100%> (+3.03%)	⬆️
...low/contrib/operators/oracle_to_oracle_transfer.py	100% <100%> (+11.11%)	⬆️
airflow/contrib/operators/s3_to_sftp_operator.py	100% <100%> (ø)	⬆️
... and 82 more

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[ryw]

@ashb why this codecov result?

[mik-laj]

We are in the process of big code reorganization. https://cwiki.apache.org/confluence/display/AIRFLOW/AIP-21%3A+Changes+in+import+paths

[ashb]

@ashb why this codecov result?

Cos codecov is confused sometimes. We don't really pay much attention to it.