fix: Closes #103 use index to generate key in submenu item

[connoratrug]

Checklist

• [ ] Functionality works & meets specifications
• [ ] Code reviewed
• [ ] Code unit/integration/system tested
• [ ] User documentation updated
• [ ] Clean commits
• [ ] No warnings during install
• [ ] Added Feature/Fix to release notes

[codecov[bot]]

Codecov Report

Merging #104 into master will not change coverage by %. The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #104   +/-   ##
======================================
  Coverage    93.0%   93.0%           
======================================
  Files          18      18           
  Lines         144     144           
  Branches       20      19    -1     
======================================
  Hits          134     134           
  Misses         10      10           

Flag	Coverage Δ
#unit	93.0% <ø> (ø)

Impacted Files	Coverage Δ
src/components/DropDownItems.vue	100.0% <ø> (ø)

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[molgenis-jenkins]

:tada: This PR is included in version 1.6.4 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: