[AIRFLOW-6630] Bump handlebars to resolve handlebars advisory

[ryw]

Bump Handlebars to 4.3.5 to resolve advisory
https://www.npmjs.com/advisories/1324

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Issue link: AIRFLOW-6630

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 #7284 into master will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #7284      +/-   ##
=========================================
+ Coverage   85.45%   85.5%   +0.05%     
=========================================
  Files         841     864      +23     
  Lines       40363   40455      +92     
=========================================
+ Hits        34491   34592     +101     
+ Misses       5872    5863       -9

Impacted Files	Coverage Δ
airflow/operators/mysql_to_hive.py	0% <0%> (-100%)	⬇️
airflow/operators/s3_to_hive_operator.py	0% <0%> (-93.97%)	⬇️
airflow/contrib/operators/s3_to_sftp_operator.py	100% <0%> (ø)	⬆️
airflow/operators/google_api_to_s3_transfer.py	100% <0%> (ø)	⬆️
airflow/contrib/operators/hive_to_dynamodb.py	100% <0%> (ø)	⬆️
airflow/contrib/operators/file_to_wasb.py	100% <0%> (ø)	⬆️
airflow/operators/mssql_to_hive.py	100% <0%> (ø)	⬆️
...irflow/contrib/operators/gcs_to_gdrive_operator.py	100% <0%> (ø)	⬆️
airflow/contrib/operators/gcs_to_s3.py	100% <0%> (ø)	⬆️
airflow/operators/hive_to_samba_operator.py	100% <0%> (ø)	⬆️
... and 38 more

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[ryw]

just rebased this branch to master