Use Path.posix to ensure we'll get forward slashes even on Windows

src/api-client.ts

@@ -58,7 +58,7 @@ export class CortexApiClient {
       throw new Error("Request body too large");
     }
 
-    const url = Path.join(this.apiUrl, this.apiVersion, "org", this.org, path);
+    const url = Path.posix.join(this.apiUrl, this.apiVersion, "org", this.org, path);
     return fetch(url, {
       method,
       headers: {