[Docs] Update api.asciidoc (#29166)

B16-1DEA · Christoph Büscher · commit 08c530907a9f · 2018-03-21T10:14:26.000+01:00
The parent page has the same title, and the URL path indicates this is about 
API changes, so include "API" in the title.
diff --git a/docs/reference/migration/migrate_7_0/api.asciidoc b/docs/reference/migration/migrate_7_0/api.asciidoc
@@ -1,5 +1,5 @@
 [[breaking_70_api_changes]]
-=== Breaking changes in 7.0
+=== Breaking API changes in 7.0
 
 ==== Camel case and underscore parameters deprecated in 6.x have been removed
 A  number of duplicate parameters deprecated in 6.x have been removed from
