[docs] bump bundled rack to 2.2.22

Author: chadlwilson

CHANGELOG.md

@@ -34,7 +34,7 @@ Breaking configuration capability changes
 ## 1.2.7 (UNRELEASED)
 
 - Fix ability to include and forward to JSPs under Rails (#370)
-- Update (bundled) rack to 2.2.21 (#374)
+- Update (bundled) rack to 2.2.22 (#374)
 
 ## 1.2.6