fix: report actual version instead of hardcoded 3.0.0-dev (#63)

The / endpoint was hardcoded to return 3.0.0-dev. Now uses the git tag version set via ldflags at build time.

Reviewed-on: #63
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

.woodpecker/docker.yaml

@@ -8,6 +8,8 @@ steps:
     settings:
       registry: git.unkin.net
       repo: git.unkin.net/unkin/artifactapi
+      build_args:
+        VERSION: ${CI_COMMIT_TAG}
       username: droneci
       password:
         from_secret: DRONECI_PASSWORD