Fix schedule links to sessions.

At present schedule links are pointing to `schedule/...` whereas they
should point to `sessions/...`.

Change-Id: I5f969ecc1b8cdfb98dcaf3abb764dd22417bb5c6

schedule.md

diff --git a/schedule.md b/schedule.md
index b556157..005834a 100644
--- a/schedule.md
+++ b/schedule.md
@@ -33,7 +33,7 @@
 | 18:00     | 09:00     | [Tailor Gerrit's healthcheck with Extensible Checks](sessions/extensible-healthcheck.md)
 | 18:15     | 09:15     | [Entering the gerrit world, painpoints and wows](lightning-talks/entering-gerrit-worls.md)
 | 18:30     | 09:30     | *LIGHTNING TALKS*
-| 18:45     | 09:45     | [Code Review Research Highlights](schedule/recent-rebels-research.md)
+| 18:45     | 09:45     | [Code Review Research Highlights](sessions/recent-rebels-research.md)
 | 19:30     | 10:00     | End of Day 1 - Sweden / Break & Networking - US
 | 20:00     |           | Dinner - Celebrations for Gerrit 15 years - Sweden
 |           | 10:30     | [Git GC at scale for Pro](sessions/git-gc-at-scale.md)