fix: typing file for compute builtin (#1028)

Author: Guy Bedford

test-d/compute.test-d.ts

@@ -0,0 +1,9 @@
+/// <reference path="../types/compute.d.ts" />
+import { vCpuTime, purgeSurrogateKey } from 'fastly:compute';
+import { expectType } from 'tsd';
+
+// Compute
+{
+  expectType<number>(vCpuTime());
+  expectType<boolean>(purgeSurrogateKey('boo'));
+}

types/compute.d.ts

@@ -10,5 +10,8 @@ declare module 'fastly:compute' {
    * @param soft - Enable to perform a soft purge, retaining stale cache entries to
    *               reduce load on the origin server, defaults to a hard purge.
    */
-  export function purgeSurrogateKey(surrogateKey: string, soft?: boolean);
+  export function purgeSurrogateKey(
+    surrogateKey: string,
+    soft?: boolean,
+  ): boolean;
 }