Use path.posix for static base

Since this is a web path and not platform-dependent.

Author: code-asher

src/node/http.ts

@@ -37,7 +37,7 @@ export const createClientConfiguration = (req: express.Request): ClientConfigura
 
   return {
     base,
-    csStaticBase: normalize(path.join(base, "_static/")),
+    csStaticBase: normalize(path.posix.join(base, "_static/")),
     codeServerVersion,
   }
 }