Keep continue using '2.5' stream.

This allows to use specific stream name instead of the name derived from
stream branch name.

Related: rhbz#1688758

ruby.yaml

@@ -11,6 +11,7 @@ data:
         object-oriented programming.  It has many features to process text
         files and to do system management tasks (as in Perl).  It is simple,
         straight-forward, and extensible.
+    stream: 2.5
     license:
         module:
             - MIT