Use strict everywhere (#68)

src/base.ts

@@ -1,3 +1,5 @@
+'use strict';
+
 import https, { RequestOptions } from 'https';
 import { URL } from 'url';
 import {

src/client/auth_client.ts

@@ -1,3 +1,5 @@
+'use strict';
+
 /**
  * Defines the main interface for all clients that generate credentials.
  */

src/utils.ts

@@ -1,3 +1,5 @@
+'use strict';
+
 import { promises as fs } from 'fs';
 import crypto from 'crypto';
 import path from 'path';

tests/client/credentials_json_client.test.ts

@@ -1,3 +1,5 @@
+'use strict';
+
 import 'mocha';
 import { expect } from 'chai';
 

tests/client/workload_identity_client.test.ts

@@ -1,3 +1,5 @@
+'use strict';
+
 import 'mocha';
 import { expect } from 'chai';