Update changelog for elixir-editors#415

Author: axelson

CHANGELOG.md

@@ -1,5 +1,8 @@
 ### Unreleased
 
+Improvements:
+- Add support for `textDocument/implementation` ("Go to Implmentations" and "Peek Implementations") (thanks [Łukasz Samson](https://github.com/lukaszsamson)) [#415](https://github.com/elixir-lsp/elixir-ls/pull/415)
+
 Bug Fixes:
 - Fix multiple issues with text synchronization (thanks [Łukasz Samson](https://github.com/lukaszsamson)) [#411](https://github.com/elixir-lsp/elixir-ls/pull/411)
 - Purge consolidated protocols before compilation (thanks [Łukasz Samson](https://github.com/lukaszsamson)) [#406](https://github.com/elixir-lsp/elixir-ls/pull/406)