Update pkgdown site logo (#196)

**What changes are proposed in this pull request?**
* Updated logo throughout pkgdown site. (#193)

Closes #193 


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Pre-review Checklist (if item does not apply, mark is as complete)
- [x] **All** GitHub Action workflows pass with a ✅
- [x] PR branch has pulled the most recent updates from master branch:
`usethis::pr_merge_main()`
- [x] If a bug was fixed, a unit test was added.
- [x] If a new `ard_*()` function was added, it passes the ARD
structural checks from `cards::check_ard_structure()`.
- [x] If a new `ard_*()` function was added, `set_cli_abort_call()` has
been set.
- [x] If a new `ard_*()` function was added and it depends on another
package (such as, `broom`), `is_pkg_installed("broom", reference_pkg =
"cardx")` has been set in the function call and the following added to
the roxygen comments: `@examplesIf
do.call(asNamespace("cardx")$is_pkg_installed, list(pkg = "broom"",
reference_pkg = "cardx"))`
- [x] Code coverage is suitable for any new functions/features
(generally, 100% coverage for new code): `devtools::test_coverage()`

Reviewer Checklist (if item does not apply, mark is as complete)

- [ ] If a bug was fixed, a unit test was added.
- [ ] Code coverage is suitable for any new functions/features:
`devtools::test_coverage()`

When the branch is ready to be merged:
- [ ] Update `NEWS.md` with the changes from this pull request under the
heading "`# cardx (development version)`". If there is an issue
associated with the pull request, reference it in parentheses at the end
update (see `NEWS.md` for examples).
- [ ] **All** GitHub Action workflows pass with a ✅
- [ ] Approve Pull Request
- [ ] Merge the PR. Please use "Squash and merge" or "Rebase and merge".