test(lib): update TableColumn spec

- Updates the unit tests (spec) of `TableColumn` so that they can work
  with `@vue/test-utils` V2:
    - Replaces `find` with `findComponent` because `find` is dedicated
      to DOM elements on `@vue/test-utils` V2.
    - Replaces `wrapper.name()` with `wrapper.vm.$options.name` because
      `wrapper.name` no longer exists in `@vue/test-utils` V2.
    - Replaces the test on `wrapper.isVueInstance` with presence of
      `wrapper.vm` because `wrapper.isVueInstance` no longer exists in
      `@vue/test-utils` V2.
    - Removes the `sync` option for `mount` because it no longer exists
      in `@vue/test-utils`. It neither has any effect.

issue #1

src/components/table/TableColumn.spec.js

@@ -17,11 +17,11 @@ const WrapperComp = {
 
 describe('BTableColumn', () => {
     beforeEach(() => {
-        wrapper = mount(WrapperComp, { sync: false }).find({ ref: 'testItem' })
+        wrapper = mount(WrapperComp).findComponent({ ref: 'testItem' })
     })
 
     it('is called', () => {
-        expect(wrapper.name()).toBe('BTableColumn')
-        expect(wrapper.isVueInstance()).toBeTruthy()
+        expect(wrapper.vm).toBeTruthy()
+        expect(wrapper.vm.$options.name).toBe('BTableColumn')
     })
 })