Fix Shellcheck SC2155: Declare + export separately

Declare and assign separately to avoid masking return values.

https://github.com/koalaman/shellcheck/wiki/SC2155

Signed-off-by: Dan Callahan <danc@element.io>

demo/start.sh

@@ -8,7 +8,8 @@ cd "$DIR/.." || exit
 
 mkdir -p demo/etc
 
-export PYTHONPATH=$(readlink -f "$(pwd)")
+PYTHONPATH=$(readlink -f "$(pwd)")
+export PYTHONPATH
 
 
 echo $PYTHONPATH