docs: fix code block (#78)

docs/content/proxy-service/0.installation.md

@@ -118,7 +118,7 @@ In the same file, define a proxy service for our `TodosRepo`:
 export const [registerTodosRepo, getTodosRepo] = defineProxyService('TodosRepo', createTodosRepo);
 ```
 
-:::
+::
 
 Now that you have a service implemented, we need to tell the extension to use it! This needs to happen syncronously when your background script is loaded, so put it as high up as possible.