Merge pull request open-mpi#5112 from bwbarrett/v3.1.x-VERSION

dist: Set version to 3.1.0rc6

Author: bwbarrett

VERSION

@@ -26,7 +26,7 @@ release=0
 # requirement is that it must be entirely printable ASCII characters
 # and have no white space.
 
-greek=rc5
+greek=rc6
 
 # If repo_rev is empty, then the repository version number will be
 # obtained during "make dist" via the "git describe --tags --always"