Fix typo in stale session check [#2404 state:resolved]

actionpack/lib/action_dispatch/middleware/session/abstract_store.rb

@@ -74,7 +74,7 @@ def stale_session_check!
                 # Note that the regexp does not allow $1 to end with a ':'
                 $1.constantize
               rescue LoadError, NameError => const_error
-                raise ActionController::SessionRestoreError, "Session contains objects whose class definition isn\\'t available.\nRemember to require the classes for all objects kept in the session.\n(Original exception: \#{const_error.message} [\#{const_error.class}])\n"
+                raise ActionController::SessionRestoreError, "Session contains objects whose class definition isn't available.\nRemember to require the classes for all objects kept in the session.\n(Original exception: #{const_error.message} [#{const_error.class}])\n"
               end
 
               retry