Silent shelljs by default

Shelljs likes to report some warnings, which we do not want to show to our users.
So set it to silent mode by default. In case for any shelljs command you want to show the warnings, just set silent to false before executing it.

Author: rosen-vladimirov

lib/common

@@ -7,6 +7,8 @@ require("./common/verify-node-version").verifyNodeVersion(require("../package.js
 require("./bootstrap");
 import * as fiber from "fibers";
 import Future = require("fibers/future");
+import * as shelljs from "shelljs";
+shelljs.config.silent = true;
 import {installUncaughtExceptionListener} from "./common/errors";
 installUncaughtExceptionListener(process.exit);