message: Update CONTRIBUTING.md to modern standards
diff: @@ -3,7 +3,6 @@ A good issue can mean the difference between a quick fix and a long, painful fix
  following guidelines exist:
  - Use the [Github issue tracker](https://github.com/matrix-org/matrix-appservice-irc/issues) to file your issues.
  - Do **not** use the matrix.org JIRA project.
  - Write a short title which neatly summaries the *problem*. Do **not** write the *solution* in the issue title.
  For example: `Cannot create a nick with | in it` is a good issue title. `Filter nicks according to RFC 2812`
  is not a good issue title.
  @@ -38,17 +37,12 @@ This project follows "git flow" semantics. In practice, this means:
  - Make sure your new code passes all the code checks (tests and linting). Do this by running
  `npm run check`.
  - Create a pull request. If this PR fixes an issue, link to it by referring to its number.
  + - PRs from community members must be signed off as per Synapse's [Attribution section](https://github.com/matrix-org/synapse/blob/master/CONTRIBUTING.rst#attribution)
  ## Coding notes
  -The IRC bridge is compatible on Node.js v4+. It does not use a transpiler like Babel. As such,
  -only a subset of ES6 features are natively supported. Some of the common ones which are supported
  -are listed below (see http://node.green/ for the full list):
  - - Generators
  - - \`template ${strings}\`
  - - ES6 `class`es
  - - `let`, `const`
  - - `Map`, `Set`
  - - `(arrow) => { } // functions`
  +The IRC bridge is compatible on Node.js v10+. Buildkite is used to ensure that tests will run on
  +supported environments. Code should not use any ES features greater than that supported in ES2018.
  +Please see http://node.green/ for a list of supported features.
  Tests are written in Jasmine. Depending on the pull request, you may be asked to write tests for
  new code.
  @@ -58,3 +52,4 @@ new code.
  - Each formal release corresponds to a branch which is of the form `vX.Y.Z` where `X.Y.Z` maps
  directly onto the `package.json` (NPM) version.
  - Releases are also tagged so they are present on the Releases page on Github.
  + - Releases should always be signed by the maintainers key
  \ No newline at end of file
  