Enhance definition for heapdump (#24927)

* Enhance definition and according tests for heapdump

* Add changes to fix the CI

types/heapdump/heapdump-tests.ts

@@ -1,9 +1,20 @@
 import * as heapdump from 'heapdump';
 
-heapdump.writeSnapshot('/tmp/myDump', (err) => {
-  if (err) {
-    console.log('Failed to dump heap: ' + err);
-  } else {
-    console.log('Successfully dumped heap!');
-  }
+let strValue = "";
+let errValue = new Error(strValue);
+let nullValue = null;
+let undefinedValue;
+
+heapdump.writeSnapshot(strValue, (err, filename) => {
+  errValue = err as Error;
+  nullValue = err as null;
+  strValue = filename as string;
+  undefinedValue = filename as undefined;
+});
+
+heapdump.writeSnapshot((err, filename) => {
+  errValue = err as Error;
+  nullValue = err as null;
+  strValue = filename as string;
+  undefinedValue = filename as undefined;
 });

types/heapdump/index.d.ts

@@ -2,5 +2,7 @@
 // Project: https://github.com/bnoordhuis/node-heapdump
 // Definitions by: weekens <https://github.com/weekens>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
+// TypeScript Version: 2.1
 
-export function writeSnapshot(dumpFileName: string, callback: (err?: Error) => void): void;
+export function writeSnapshot(dumpFileName?: string, callback?: (err: Error | null, filename: string | undefined) => void): void;
+export function writeSnapshot(callback: (err: Error | null, filename: string | undefined) => void): void;