Update timestamp ready for tag

Not currently used. Just getting into the habit of updating it when I
tag a release.
diff --git a/build.properties.default b/build.properties.default
index 14c75d6..76e89d8 100644
--- a/build.properties.default
+++ b/build.properties.default
@@ -31,8 +31,8 @@
 
 # ----- Reproducible builds -----
 # Uncomment and set to current time for reproducible builds
-#2021-07-29T12:00:00Z
-#ant.tstamp.now=1627560000
+#2021-08-03T18:00:00Z
+#ant.tstamp.now=1628013600
 
 # ----- Source control flags -----
 git.branch=main