Merge pull request reduxjs#713 from leoasis/add_redux-immutable-state-invariant_to_ecosystem

Add redux-immutable-state-invariant to Ecosystem.md

Author: gaearon

docs/introduction/Ecosystem.md

@@ -18,6 +18,7 @@ On this page we will only feature a few of them that the Redux maintainers have
 * [redux-rx](https://github.com/acdlite/redux-rx) — RxJS utilities for Redux, including a middleware for Observable
 * [redux-batched-updates](https://github.com/acdlite/redux-batched-updates) — Batch React updates that occur as a result of Redux dispatches
 * [redux-logger](https://github.com/fcomb/redux-logger) — Log every Redux action and the next state
+* [redux-immutable-state-invariant](https://github.com/leoasis/redux-immutable-state-invariant) — Detects state mutations between and outside redux dispatches. For development use only.
 
 ## Components