Fix broken links in schedule

Change-Id: Id05e91badb47c6a1fe76af0833cd6bc7cbb22643

schedule.md

diff --git a/schedule.md b/schedule.md
index 86fa498..7335b24 100644
--- a/schedule.md
+++ b/schedule.md
@@ -22,9 +22,9 @@
 | 11:45    | [JGit reftable in Gerrit: past, present and future adoption](sessions/reftable.md)                               |
 | 12:10    | [How to do code review like a pro (15 mins)](lightning-talks/how-to-code-review.md)                              |
 | 12:40    | Lunch & Networking                                                                                               |
-| 14:10    | [Characterizing the Prevalence, Distribution, and Duration of Stale Reviewer Recommendations](sessions/characterizing-stale-reviewer-recommendations.md) |
+| 14:10    | [Characterizing the Prevalence, Distribution, and Duration of Stale Reviewer Recommendations](sessions/characterizing-stale-reviewer-recommendations.md)|
 | 15:00    | [GitButler](sessions/gitbutler.md)                                                                               |
-| 15:30    | [Contributing to Gerrit: challenges and rewards of Open Source development](sessions/contributing-to-gerrit.md)  |
+| 15:30    | [Contributing to Gerrit: challenges and rewards of Open Source development](lightning-talks/contributing-to-gerrit.md)|
 | 15:45    | Break                                                                                                            |
 | 16:00    | Q&A with the maintainers                                                                                         |
 | 16:45    | [Scaling Gerrit: JVM Tuning, Upgrades, and Architecture Enhancements from the SRE Perspective](sessions/scaling-gerrit.md)|

sessions/reftable-backend.md

diff --git a/sessions/reftable-backend b/sessions/reftable-backend.md
similarity index 100%
rename from sessions/reftable-backend
rename to sessions/reftable-backend.md