Fix changelog headings

Author: jasongrout

CHANGELOG.md

@@ -9,13 +9,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [1.0] - 2020-9-18
 
-## Added.
+### Added.
 
 * Added a basic, styled `login.html` template. ([220](https://github.com/jupyter/jupyter_server/pull/220), [295](https://github.com/jupyter/jupyter_server/pull/295))
 * Added new extension manager API for handling server extensions. ([248](https://github.com/jupyter/jupyter_server/pull/248), [265](https://github.com/jupyter/jupyter_server/pull/265), [275](https://github.com/jupyter/jupyter_server/pull/275), [303](https://github.com/jupyter/jupyter_server/pull/303))
 * The favicon and Jupyter logo are now available under jupyter_server's static namespace. ([284](https://github.com/jupyter/jupyter_server/pull/284))
 
-## Changed.
+### Changed.
 
 * `load_jupyter_server_extension` should be renamed to `_load_jupyter_server_extension` in server extensions. Server now throws a warning when the old name is used. ([213](https://github.com/jupyter/jupyter_server/pull/213))
 * Docs for server extensions now recommend using `authenticated` decorator for handlers. ([219](https://github.com/jupyter/jupyter_server/pull/219))
@@ -25,11 +25,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * Dropped support for Python 3.5. ([296](https://github.com/jupyter/jupyter_server/pull/296))
 * Made the `config_dir_name` trait configurable in `ConfigManager`. ([297](https://github.com/jupyter/jupyter_server/pull/297))
 
-## Removed for now removed features.
+### Removed for now removed features.
 
 * Removed ipykernel as a dependency of jupyter_server. ([255](https://github.com/jupyter/jupyter_server/pull/255))
 
-## Fixed for any bug fixes.
+### Fixed for any bug fixes.
 * Prevent a re-definition of prometheus metrics if `notebook` package already imports them. ([#210](https://github.com/jupyter/jupyter_server/pull/210))
 * Fixed `terminals` REST API unit tests that weren't shutting down properly. ([221](https://github.com/jupyter/jupyter_server/pull/221))
 * Fixed jupyter_server on Windows for Python < 3.7. Added patch to handle subprocess cleanup. ([240](https://github.com/jupyter/jupyter_server/pull/240))