message: fix(server): fixes explorer app redirect url registration
  now using proper url concatenation
diff: @@ -79,7 +79,7 @@ let SpeckleApiExplorer = {
  description: 'GraphiQL Playground with authentication.',
  trustByDefault: true,
  public: true,
  - redirectUrl: `${process.env.CANONICAL_URL}/explorer`,
  + redirectUrl: ( new URL( '/explorer', process.env.CANONICAL_URL ) ).toString(),
  scopes: 'all'
  }
  