7 char sha in changelog

CHANGES.rst

@@ -1,7 +1,7 @@
 Changes in synapse v0.31.0 (2018-06-06)
 =======================================
 
-Most notable change is to switch to python prometheus library to improve system
+Most notable change from v0.30.0 is to switch to python prometheus library to improve system
 stats reporting. WARNING this changes a number of prometheus metrics in a
 backwards-incompatible manner. For more details, see
 `docs/metrics-howto.rst <docs/metrics-howto.rst#removal-of-deprecated-metrics--time-based-counters-becoming-histograms-in-0310>`_.
@@ -9,8 +9,8 @@ backwards-incompatible manner. For more details, see
 Bug Fixes:
 
 * Fix metric documentation tables (PR #3341)
-* Fix LaterGuage error handling (694968fa81aab4eac81309b1e16f6063103dd57f)
-* Fix replication metrics (b7e7fd2d0edd4d46aaf9d6afc8df14cf3de911f9)
+* Fix LaterGuage error handling (694968f)
+* Fix replication metrics (b7e7fd2)
 
 Changes in synapse v0.31.0-rc1 (2018-06-04)
 ==========================================