Process no exitCode (#10778)

According to [node.js v4 doc - exitCode](https://nodejs.org/dist/latest-v4.x/docs/api/process.html#process_process_exitcode), there is exitCode in Process.

node/node-4.d.ts

@@ -290,6 +290,7 @@ declare namespace NodeJS {
         cwd(): string;
         env: any;
         exit(code?: number): void;
+        exitCode: number;
         getgid(): number;
         setgid(id: number): void;
         setgid(id: string): void;