docs(contributing): replaces slack link with spectrum link (#2932)

* docs(contributing): replaces slack link with spectrum link

* Changelog update

Author: afenton90

CONTRIBUTING.md

@@ -4,7 +4,7 @@ Excited about Apollo and want to make it better? We’re excited too!
 
 Apollo is a community of developers just like you, striving to create the best tools and libraries around GraphQL. We welcome anyone who wants to contribute or provide constructive feedback, no matter the age or level of experience. If you want to help but don't know where to start, let us know, and we'll find something for you.
 
-Oh, and if you haven't already, sign up for the [Apollo Slack](http://www.apollodata.com/#slack).
+Oh, and if you haven't already, sign up for the [Apollo Spectrum](https://spectrum.chat/apollo).
 
 Here are some ways to contribute to the project, from easiest to most difficult:
 

Changelog.md

@@ -11,6 +11,11 @@
   data preserved when the components tree is re-rendered.  <br/>
   [@hwillson](https://github.com/hwillson) in [#2914](https://github.com/apollographql/react-apollo/pull/2914)
 
+### Improvements
+
+- Documentation updates.  <br/>
+  [@afenton90](https://github.com/afenton90) in [#2932](https://github.com/apollographql/react-apollo/pull/2932)
+
 
 ## 2.5.3