docs: update current version to 5.1

docs/versions.json

@@ -1,6 +1,6 @@
 [
-  { "version": "v5.1", "path": "/v5.1", "archived": false },
-  { "version": "v5.0", "path": "/", "archived": false, "current": true },
+  { "version": "v5.1", "path": "/", "archived": false, "current": true },
+  { "version": "v5.0", "path": "/v5.0", "archived": true },
   { "version": "v4.6", "path": "/v4.6", "archived": true },
   { "version": "v4.5", "path": "/v4.5", "archived": true },
   { "version": "v4.4", "path": "/v4.4", "archived": true },