update changelog

#940 confirmed fix

Author: sumneko

Diff for: changelog.md

@@ -4,6 +4,7 @@
 * `CHG` completion: reduced sorting priority for postfix completion
 * `FIX` [#936](https://github.com/sumneko/lua-language-server/issues/936)
 * `FIX` [#937](https://github.com/sumneko/lua-language-server/issues/937)
+* `FIX` [#940](https://github.com/sumneko/lua-language-server/issues/940)
 * `FIX` [#941](https://github.com/sumneko/lua-language-server/issues/941)
 * `FIX` [#941](https://github.com/sumneko/lua-language-server/issues/942)
 * `FIX` [#943](https://github.com/sumneko/lua-language-server/issues/943)