bump: release 0.16 (#678)

Signed-off-by: Billy Zha <jinzha1@microsoft.com>

Author: qweeah

internal/version/version.go

@@ -17,7 +17,7 @@ package version
 
 var (
 	// Version is the current version of the oras.
-	Version = "0.15.0"
+	Version = "0.16.0"
 	// BuildMetadata is the extra build time data
 	BuildMetadata = "unreleased"
 	// GitCommit is the git sha1