Add a HACK comment

packages/0x.js/test/global_hooks.ts

@@ -6,6 +6,8 @@ import { constants } from './utils/constants';
 import { provider } from './utils/web3_wrapper';
 
 before('migrate contracts', async function() {
+    // HACK: Since the migrations take longer then our global mocha timeout limit
+    // we manually increase it for this before hook.
     this.timeout(20000);
     const defaults = {
         gas: devConstants.GAS_ESTIMATE,