update readme to add credits and call for collaborators (#540)

* also pin chai-string to ~1.3.0 as chai-string 1.5.0 introduce a breaking change that breaks our node v4 CI.

README.md

@@ -8,6 +8,8 @@ node-fetch
 
 A light-weight module that brings `window.fetch` to Node.js
 
+(We are looking for [v2 maintainers and collaborators](https://github.com/bitinn/node-fetch/issues/252))
+
 <!-- TOC -->
 
 - [Motivation](#motivation)
@@ -470,6 +472,8 @@ An operational error in the fetching process. See [ERROR-HANDLING.md][] for more
 
 Thanks to [github/fetch](https://github.com/github/fetch) for providing a solid implementation reference.
 
+`node-fetch` v1 was maintained by [@bitinn](https://github.com/bitinn), v2 is currently maintained by [@TimothyGu](https://github.com/timothygu), v2 readme is written by [@jkantr](https://github.com/jkantr).
+
 ## License
 
 MIT

package.json

@@ -44,7 +44,7 @@
     "chai": "^3.5.0",
     "chai-as-promised": "^7.1.1",
     "chai-iterator": "^1.1.1",
-    "chai-string": "^1.3.0",
+    "chai-string": "~1.3.0",
     "codecov": "^3.0.0",
     "cross-env": "^5.1.3",
     "form-data": "^2.3.1",