Fix vue warn about unknow custom element jhi-sort-indicator

[pascalgrimaud]

It's for removing this warning during npm test :

 PASS  src/test/javascript/spec/app/entities/test-root/operation/operation.component.spec.ts (216 MB heap size)
  ● Console

    console.error node_modules/vue/dist/vue.runtime.common.dev.js:621
      [Vue warn]: Unknown custom element: <jhi-sort-indicator> - did you register the component correctly? For recursive components, make sure to provide the "name" option.

      found in

      ---> <Operation>
             <Root>
    console.error node_modules/vue/dist/vue.runtime.common.dev.js:621

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