fix mime type

Author: mbostock

src/preview.ts

@@ -72,7 +72,7 @@ export class Server {
       if (pathname === "/_observablehq/runtime.js") {
         send(req, "/@observablehq/runtime/dist/runtime.js", {root: "./node_modules"}).pipe(res);
       } else if (pathname === "/_observablehq/client.js") {
-        end(req, res, await rollupClient("./src/client/preview.js"), "text/javascript");
+        end(req, res, await rollupClient("./src/client/preview.js"), "application/javascript");
       } else if (pathname.startsWith("/_observablehq/")) {
         send(req, pathname.slice("/_observablehq".length), {root: publicRoot}).pipe(res);
       } else if (pathname.startsWith("/_import/")) {
@@ -84,7 +84,7 @@ export class Server {
           if (!isEnoent(error)) throw error;
           throw new HttpError("Not found", 404);
         }
-        end(req, res, rewriteModule(js, file, createImportResolver(this.root)), "text/javascript");
+        end(req, res, rewriteModule(js, file, createImportResolver(this.root)), "application/javascript");
       } else if (pathname.startsWith("/_file/")) {
         const path = pathname.slice("/_file".length);
         const filepath = join(this.root, path);