Bump the inject cider-nrepl version

Author: bbatsov

cider.el

@@ -420,7 +420,7 @@ the artifact.")
 (defconst cider-latest-clojure-version "1.10.1"
   "Latest supported version of Clojure.")
 
-(defconst cider-required-middleware-version "0.28.5"
+(defconst cider-required-middleware-version "0.28.6"
   "The CIDER nREPL version that's known to work properly with CIDER.")
 
 (defcustom cider-injected-middleware-version cider-required-middleware-version