Use lolex for faking date in tests (#491)

Sinon.JS provides a project called lolex to handle faking dates. This
change replaces the fakeDate utility with the equivalent Sinon.JS code.

package.json

@@ -4,7 +4,7 @@
   "description": "JSON Web Token implementation (symmetric and asymmetric)",
   "main": "index.js",
   "scripts": {
-    "test": "nyc --reporter=html --reporter=text mocha --require test/util/fakeDate && nsp check && cost-of-modules"
+    "test": "nyc --reporter=html --reporter=text mocha && nsp check && cost-of-modules"
   },
   "repository": {
     "type": "git",
@@ -37,7 +37,7 @@
     "mocha": "^2.1.0",
     "nsp": "^2.6.2",
     "nyc": "^11.8.0",
-    "sinon": "^1.15.4"
+    "sinon": "^6.0.0"
   },
   "engines": {
     "npm": ">=1.4.28",

test/jwt.asymmetric_signing.tests.js

@@ -5,6 +5,7 @@ var path = require('path');
 var expect = require('chai').expect;
 var assert = require('chai').assert;
 var ms = require('ms');
+var sinon = require('sinon');
 
 function loadKey(filename) {
   return fs.readFileSync(path.join(__dirname, filename));
@@ -140,14 +141,14 @@ describe('Asymmetric Algorithms', function(){
 
 
         it('should valid when date are equals', function (done) {
-          Date.fix(1451908031);
+          var fakeClock = sinon.useFakeTimers({now: 1451908031});
 
           token = jwt.sign({ foo: 'bar' }, priv, { algorithm: algorithm, notBefore: 0 });
 
           jwt.verify(token, pub, function (err, decoded) {
+            fakeClock.uninstall();
             assert.isNull(err);
             assert.isNotNull(decoded);
-            Date.unfix();
             done();
           });
         });