[docs] update links for developer chatroom (#2160)

Author: odow

README.md

@@ -1,8 +1,8 @@
 # MathOptInterface
 
-| **Documentation** | **Build Status** | **Social** |
-|:-----------------:|:----------------:|:----------:|
-| [![][docs-stable-img]][docs-stable-url] [![][docs-dev-img]][docs-dev-url] | [![Build Status][build-img]][build-url] [![Codecov branch][codecov-img]][codecov-url] | [![Gitter][gitter-img]][gitter-url] [<img src="https://upload.wikimedia.org/wikipedia/commons/thumb/a/af/Discourse_logo.png/799px-Discourse_logo.png" width="64">][discourse-url] |
+| **Documentation** | **Build Status** |
+|:-----------------:|:----------------:|
+| [![][docs-stable-img]][docs-stable-url] [![][docs-dev-img]][docs-dev-url] | [![Build Status][build-img]][build-url] [![Codecov branch][codecov-img]][codecov-url] |
 
 An abstraction layer for mathematical optimization solvers. Replaces [MathProgBase](https://github.com/JuliaOpt/MathProgBase.jl).
 
@@ -16,10 +16,6 @@ An abstraction layer for mathematical optimization solvers. Replaces [MathProgBa
 [codecov-img]: http://codecov.io/github/JuMP-dev/MathOptInterface.jl/coverage.svg?branch=master
 [codecov-url]: http://codecov.io/github/JuMP-dev/MathOptInterface.jl?branch=master
 
-[gitter-url]: https://gitter.im/JuliaOpt/JuMP-dev?utm_source=share-link&utm_medium=link&utm_campaign=share-link
-[gitter-img]: https://badges.gitter.im/JuliaOpt/JuMP-dev.svg
-[discourse-url]: https://discourse.julialang.org/c/domain/opt
-
 ## Citing MathOptInterface
 
 If you find MathOptInterface useful in your work, we kindly request that you cite the
@@ -37,4 +33,4 @@ following [paper](https://pubsonline.informs.org/doi/10.1287/ijoc.2021.1067):
     publisher={INFORMS}
 }
 ```
-A preprint of this paper is [freely available](https://arxiv.org/abs/2002.03447). 
+A preprint of this paper is [freely available](https://arxiv.org/abs/2002.03447).

docs/src/submodules/Test/overview.md

@@ -308,4 +308,4 @@ submit the PR for review.
 
 !!! tip
     If you need help writing a test, [open an issue on GitHub](https://github.com/jump-dev/MathOptInterface.jl/issues/new),
-    or ask the [Developer Chatroom](https://app.gitter.im/#/room/#JuliaOpt_JuMP-dev:gitter.im)
+    or ask the [Developer Chatroom](https://jump.dev/chatroom).

docs/src/tutorials/implementing.md

@@ -14,9 +14,9 @@ MathOptInterface for a new solver.
 !!! danger
     Implementing an interface to MathOptInterface for a new solver is a lot of
     work. Before starting, we recommend that you join the
-    [Developer chatroom](https://gitter.im/JuliaOpt/JuMP-dev) and explain a
+    [Developer chatroom](https://jump.dev/chatroom) and explain a
     little bit about the solver you are wrapping. If you have questions that are
-    not answered by this guide, please ask them in the [Developer chatroom](https://gitter.im/JuliaOpt/JuMP-dev)
+    not answered by this guide, please ask them in the [Developer chatroom](https://jump.dev/chatroom)
     so we can improve this guide.
 
 ## A note on the API
@@ -62,7 +62,7 @@ MathOptInterface may not be the right tool for the job.
 
 !!! tip
     If you're not sure whether you should write an interface, ask in the
-    [Developer chatroom](https://gitter.im/JuliaOpt/JuMP-dev).
+    [Developer chatroom](https://jump.dev/chatroom).
 
 ### Find a similar solver already wrapped
 
@@ -75,7 +75,7 @@ has a good list of solvers, along with the problem classes they support.
 
 !!! tip
     If you're not sure which solver is most similar, ask in the
-    [Developer chatroom](https://gitter.im/JuliaOpt/JuMP-dev).
+    [Developer chatroom](https://jump.dev/chatroom).
 
 ### Create a low-level interface
 
@@ -106,7 +106,7 @@ are the [COIN-OR solvers](https://github.com/JuliaPackaging/Yggdrasil/tree/maste
 
 !!! warning
     Building the solver via Yggdrasil is non-trivial. Please ask the
-    [Developer chatroom](https://gitter.im/JuliaOpt/JuMP-dev) for help.
+    [Developer chatroom](https://jump.dev/chatroom) for help.
 
 If the code is commercial or not publicly available, the user will need to
 manually install the solver. See [Gurobi.jl](https://github.com/jump-dev/Gurobi.jl)
@@ -125,7 +125,7 @@ Sometimes, you will need to make manual modifications to the resulting files.
 
 #### Solvers written in other languages
 
-Ask the [Developer chatroom](https://gitter.im/JuliaOpt/JuMP-dev) for advice.
+Ask the [Developer chatroom](https://jump.dev/chatroom) for advice.
 You may be able to use one of the [JuliaInterop](https://github.com/JuliaInterop)
 packages to call out to the solver.