chore: Set version to v0.9 public, mark changelog

Author: amis92

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.9.0] - 2020-05-21
+
 ### Added
 * C# 8.0 Nullable Reference Types support (NRTs) ([#111]).
 * `netstandard2.1` targets in libraries to support NRT-enabled TFMs.
@@ -111,6 +113,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 
 [Unreleased]: https://github.com/WarHub/wham/compare/v0.8.0...HEAD
+[0.9.0]: https://github.com/WarHub/wham/compare/v0.8.0...v0.9.0
 [0.8.0]: https://github.com/WarHub/wham/compare/v0.7.0...v0.8.0
 [0.7.0]: https://github.com/WarHub/wham/compare/v0.6.17...v0.7.0
 [0.6.17]: https://github.com/WarHub/wham/compare/v0.3.0...v0.6.17

version.json

@@ -1,6 +1,6 @@
 {
   "$schema": "https://raw.githubusercontent.com/AArnott/Nerdbank.GitVersioning/master/src/NerdBank.GitVersioning/version.schema.json",
-  "version": "0.9.0-alpha.{height}",
+  "version": "0.9",
   "versionHeightOffset": -1,
   "nuGetPackageVersion": {
     "semVer": 2.0