Update docs/docs/reference/contextual/context-bounds.md

Co-authored-by: Guillaume Martres <smarter@ubuntu.com>

Author: odersky

docs/docs/reference/contextual/context-bounds.md

@@ -32,7 +32,7 @@ def g[T <: B : C](x: T): R = ...
 To ease migration, context bounds in Dotty map in Scala 3.0 to old-style implicit parameters
 for which arguments can be passed either with a `(using ...)` clause or with a normal application. From Scala 3.1 on, they will map to context parameters instead, as is described above.
 
-If the source version is `future` and the `-migration` command-line option is set, any pairing of an evidence
+If the source version is `future-migration`, any pairing of an evidence
 context parameter stemming from a context bound with a normal argument will give a migration
 warning. The warning indicates that a `(using ...)` clause is needed instead. The rewrite can be
 done automatically under `-rewrite`.