docs(guide/migration): remove redundant horizontal ruler

Author: gkalpak

docs/content/guide/migration.ngdoc

@@ -15,7 +15,7 @@ which drives many of these changes.
 * Several new features, especially animations, would not be possible without a few changes.
 * Finally, some outstanding bugs were best fixed by changing an existing API.
 
-<hr />
+
 
 ## Contents