Add missing changelog entries for v4 (heroku#176)

And clean up the existing changelog slightly.

Closes heroku#175.

CHANGELOG.md

@@ -1,16 +1,30 @@
-## v3 (3/30/2017)
+# Static Buildpack Changelog
+
+## Unreleased
+
+
+## v4 (2019-09-18)
+
+* [#136](https://github.com/heroku/heroku-buildpack-static/pull/136) Add support for canonical host
+* [#45](https://github.com/heroku/heroku-buildpack-static/pull/45) Add Basic Auth Configuration
+* [#78](https://github.com/heroku/heroku-buildpack-static/pull/78) Add json mime type
+* [#70](https://github.com/heroku/heroku-buildpack-static/pull/70) Make config copying idempotent
+* [#68](https://github.com/heroku/heroku-buildpack-static/pull/68) Disable access logs
+
+## v3 (2017-03-30)
+
 * [#32](https://github.com/heroku/heroku-buildpack-static/pull/32) proxies set ssl server name extension for SNI
 * [#37](https://github.com/heroku/heroku-buildpack-static/pull/47) fallback proxies set ssl server name extension for SNI
 * [#61](https://github.com/heroku/heroku-buildpack-static/pull/61) proxy redirects work even when the scheme does not match
 * [#62](https://github.com/heroku/heroku-buildpack-static/pull/62) clean urls work even on a directory
 * [#63](https://github.com/heroku/heroku-buildpack-static/pull/63) proxies respect DNS TTL
 * [#65](https://github.com/heroku/heroku-buildpack-static/pull/65) https redirects happen over proxies
 
-## v2 (7/13/2016)
+## v2 (2016-07-13)
 
 * [#36](https://github.com/heroku/heroku-buildpack-static/pull/36) env interpolation available when doing `redirects`
 * [#40](https://github.com/heroku/heroku-buildpack-static/pull/40) mitigate CRLF HTTP Header Injection when using `https_only`
 
-## v1 (3/27/2016)
+## v1 (2016-03-27)
 
 * Initial Release!