Add missed packages in some lessons (reactjs#160)

Author: elrumordelaluz

lessons/12-navigating/package.json

@@ -12,6 +12,7 @@
   "license": "ISC",
   "dependencies": {
     "compression": "^1.6.1",
+    "express": "^4.13.4",
     "if-env": "^1.0.0",
     "react": "^0.14.7",
     "react-dom": "^0.14.7",

lessons/13-server-rendering/package.json

@@ -12,6 +12,7 @@
   "license": "ISC",
   "dependencies": {
     "compression": "^1.6.1",
+    "express": "^4.13.4",
     "if-env": "^1.0.0",
     "react": "^0.14.7",
     "react-dom": "^0.14.7",

lessons/14-whats-next/package.json

@@ -15,6 +15,7 @@
   "license": "ISC",
   "dependencies": {
     "compression": "^1.6.1",
+    "express": "^4.13.4",
     "if-env": "^1.0.0",
     "react": "^0.14.7",
     "react-dom": "^0.14.7",