ci: Fix URL associated with success status

This commit updates target-url from "github.com" to "github.io" domain.
See https://github.blog/2013-04-05-new-github-pages-domain-github-io/

Author: jcfr

.circleci/config.yml

@@ -97,7 +97,7 @@ jobs:
               --status-update-revision ${SLICER_REPO_REVISION} \
               --slicer-repo-branch "${SLICER_REPO_BRANCH}" \
               --slicer-repo-tag "${SLICER_REPO_TAG}" \
-              --status-update-target-url "https://slicer.github.com/${PUBLISH_GITHUB_PROJECT_NAME}"
+              --status-update-target-url "https://slicer.github.io/${PUBLISH_GITHUB_PROJECT_NAME}"
 
 workflows:
   version: 2