feat(react): update minimum react version supported

BREAKING CHANGE: from version `0.7.0` `@uirouter/react` only supports react from version `16.3.x` because of the new Context API.
If you need to use it with previous versions of React you should check the `0.6.x`, but bear in mind that it’s no longer supported and it’s advised to update React instead.

package.json

@@ -47,7 +47,7 @@
     "prop-types": "^15.6.1"
   },
   "peerDependencies": {
-    "react": "^15.0.0 || ^16.0.0"
+    "react": "^16.3.0"
   },
   "devDependencies": {
     "@types/classnames": "^2.2.3",