Update to webpack 3 (#471)

Now that webpack 3 is out, I am bumping some versions in here
so folks can update. I don't know if any other changes are required
but I figured I'd get the ball rolling.

package.json

@@ -16,7 +16,7 @@
   },
   "peerDependencies": {
     "babel-core": "6 || 7 || ^7.0.0-alpha || ^7.0.0-beta || ^7.0.0-rc",
-    "webpack": "2"
+    "webpack": "2 || 3"
   },
   "devDependencies": {
     "ava": "^0.19.0",
@@ -40,7 +40,7 @@
     "react-intl": "^2.1.2",
     "react-intl-webpack-plugin": "^0.0.3",
     "rimraf": "^2.4.3",
-    "webpack": "^2.2.0"
+    "webpack": "^3.0.0"
   },
   "scripts": {
     "clean": "rimraf lib/",