Fix setE3Env.bash to correctly source activate script

require-ess/tools/setE3Env.bash

 #!/usr/bin/env bash
 
 # This file exists for (temporary) backwards compatability
-echo "setE3Env.bash has been deprecated, please use activate instead"
+echo "setE3Env.bash has been deprecated, please use activate instead" >&2
 
-DIR="${0%/*}"
+DIR="${BASH_SOURCE[0]%/*}"
 # shellcheck source=require-ess/tools/activate
 . "$DIR"/activate