Release 0.21.0 (#1933)

diff --git a/version.bzl b/version.bzl
index 2cfaaeb..9087a41 100644
--- a/version.bzl
+++ b/version.bzl
@@ -1,3 +1,3 @@
 """The version of rules_rust."""
 
-VERSION = "0.20.0"
+VERSION = "0.21.0"