qapi: Change "since 2.13" annotations to "since 3.0"

We're going to make the next release be 3.0, not 2.13; change
the annotations in our json appropriately.

Changes produced with
  sed -i -e 's/2\.13/3.0/g' qapi/*.json

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-id: 20180522104000.9044-2-peter.maydell@linaro.org
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 7dfa77a..ad66ad6 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -2424,7 +2424,7 @@
 # @vxhs: Since 2.10
 # @throttle: Since 2.11
 # @nvme: Since 2.12
-# @copy-on-read: Since 2.13
+# @copy-on-read: Since 3.0
 #
 # Since: 2.9
 ##
@@ -2452,7 +2452,7 @@
 # @x-check-cache-dropped: whether to check that page cache was dropped on live
 #                         migration.  May cause noticeable delays if the image
 #                         file is large, do not use in production.
-#                         (default: off) (since: 2.13)
+#                         (default: off) (since: 3.0)
 #
 # Since: 2.9
 ##