Bump pyyaml from 5.3b1 to 5.4 in /scripts (#1318)

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Eric Beahan <eric.beahan@elastic.co>

Author: dependabot[bot]

CHANGELOG.next.md

@@ -61,7 +61,7 @@ Thanks, you're awesome :-) -->
 * Include formatting guidance and examples for MAC address fields. #456
 * New section in ECS detailing event categorization fields usage. #1242
 * `user.changes.*`, `user.effective.*`, and `user.target.*` field reuses are GA. #1271
-* Bump jinja2 from 2.11.2 to 2.11.3 #1310
+* Update Python dependencies #1310, #1318
 
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scripts/requirements.txt

@@ -1,5 +1,5 @@
 pip
-PyYAML==5.3b1
+PyYAML==5.4
 autopep8==1.4.4
 yamllint==1.19.0
 mock==4.0.2