R4R: Update reproducible build command (#1278)

* Update reproducible build command

to use latest reproducible build docker image from https://github.com/tendermint/images which is published on the tendermintdev dockerhub account

* Update RELEASING.md

* Update RELEASING.md

* Update join-mainnet.md

Makefile

@@ -112,7 +112,7 @@ build-reproducible: go.sum
         --env VERSION=$(VERSION) \
         --env COMMIT=$(COMMIT) \
         --env LEDGER_ENABLED=$(LEDGER_ENABLED) \
-        --name latest-build cosmossdk/rbuilder:latest
+        --name latest-build tendermintdev/rbuilder:latest
 	$(DOCKER) cp -a latest-build:/home/builder/artifacts/ $(CURDIR)/
 
 build-linux: go.sum

RELEASING.md

@@ -76,6 +76,8 @@ these artifacts should be included in the release.
 make distclean build-reproducible
 ```
 
+This runs the docker image [tendermintdev/rbuilder](https://hub.docker.com/r/tendermintdev/rbuilder) with a copy of the [rbuilder](https://github.com/tendermint/images/tree/master/rbuilder) docker file.
+
 Then use the following release text template:
 
 ```markdown