clean during artifact build release step 6

I think the `clean` task is important here, Felix and I were seeing
issues with jar filenames with incorrect version numbers. His work on
FINERACT-2341 may have fixed whatever was causing it, but let's
also/still do the `clean` before building release artifacts / candidates
just to be safe.

fineract-doc/src/docs/en/chapters/release/process-step06.adoc

@@ -4,17 +4,15 @@
 
 Create source and binary tarballs.
 
-// FIXME - clean this up? focus on what commands should actually be run
-
 [source,bash,subs="attributes+"]
 ----
-./gradlew --rerun-tasks srcDistTar binaryDistTar <1>
+./gradlew clean
+./gradlew srcDistTar binaryDistTar
 ----
-<1> The source tarball might not be created if `--rerun-tasks` is omitted.
 
 Look in `fineract-war/build/distributions/` for the tarballs.
 
-Make sure to do some sanity checks. The source tarball and the code in the release branch (at the commit with the release tag) should match.
+Do some sanity checks. The source tarball and the code in the release branch (at the commit with the release tag) should match.
 
 [source,bash,subs="attributes+"]
 ----
@@ -27,8 +25,6 @@ cd ..
 diff -r fineract apache-fineract-src-{revnumber}
 ----
 
-// FIXME - add output example
-
 Make sure the code compiles and tests pass on the uncompressed source. Do as much testing as you can and share what you did. Here's the bare minimum check:
 
 [source,bash,subs="attributes+"]