fix(deps): explicitely add portfinder (angular#2831)

This PR explicitely adds portfinder as a dependency.

We're using portfinder in the serve command but getting it transitively as a ember-cli dependency.

Fix angular#2755
Fix angular#2769

Author: filipesilva

package.json

@@ -86,6 +86,7 @@
     "offline-plugin": "^3.4.1",
     "opn": "4.0.1",
     "parse5": "^2.1.5",
+    "portfinder": "1.0.9",
     "postcss-discard-comments": "^2.0.4",
     "postcss-loader": "^0.9.1",
     "protractor": "^3.3.0",

packages/angular-cli/package.json

@@ -69,6 +69,7 @@
     "offline-plugin": "^3.4.1",
     "opn": "4.0.1",
     "parse5": "^2.1.5",
+    "portfinder": "1.0.9",
     "postcss-loader": "^0.9.1",
     "protractor": "^3.3.0",
     "raw-loader": "^0.5.1",