Move the release date to the next month

Seems like it's not happening this month given the amount of blockers
and also some pieces of work that have not landed yet.

docs/release_guide.pod

@@ -18,7 +18,7 @@ Note that we are trying very hard to ensure there are no backward
 compatibility issues post version 6.c. As such, we may end up delaying
 some releases to ensure any compatibility issues are resolved.
 
-  2019-09-21   Rakudo #132 (AlexDaniel + kawaii + Releasable)
+  2019-10-19   Rakudo #132 (AlexDaniel + kawaii + Releasable)
 
 (More planned dates can be generated with F<tools/release-dates.p6>).