Upgrade to React 16 (ianstormtaylor#1178)

* Allow React 16 in peerDeps and use it for dev

* Make tests pass with React 16

Changes are cosmetic:
- React 16 no longer adds a trailing `;` to `style` attributes
- React 16 outputs `0` and not `0px` for sizes in `style`

package.json

@@ -18,7 +18,7 @@
   },
   "peerDependencies": {
     "immutable": "^3.8.1",
-    "react": "^0.14.0 || ^15.0.0"
+    "react": "^0.14.0 || ^15.0.0 || ^16.0.0"
   },
   "devDependencies": {
     "babel-cli": "^6.10.1",