Bump jsonmerge from 1.8.0 to 1.9.0 in /stix_shifter (#1194)

Bumps [jsonmerge](https://github.com/avian2/jsonmerge) from 1.8.0 to 1.9.0.
- [Release notes](https://github.com/avian2/jsonmerge/releases)
- [Changelog](https://github.com/avian2/jsonmerge/blob/master/ChangeLog)
- [Commits](avian2/jsonmerge@jsonmerge-1.8.0...jsonmerge-1.9.0)

---
updated-dependencies:
- dependency-name: jsonmerge
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

stix_shifter/requirements.txt

@@ -9,7 +9,7 @@ requests_toolbelt==0.9.1
 stix2-patterns==1.3.2
 stix2-validator==3.0.2
 xmltodict==0.13.0
-jsonmerge==1.8.0
+jsonmerge==1.9.0
 json-fix==0.5.0
 colorlog==6.7.0
 stix2-matcher==3.0.0