retry: cut down to 14 from 20

I did some stats analysis a while ago, I think the odds at 14 runs of a
fail is as statistically signficant as 20? Sorry, don't remember the
math.

docker/entrypoint.sh

@@ -1,6 +1,6 @@
 #! /bin/bash
 cd lnprototest || exit
-for i in range{0..20};
+for i in range{0..14};
 do
   if make check PYTEST_ARGS='--runner=lnprototest.clightning.Runner -n4 --dist=loadfile --log-cli-level=DEBUG'; then
     echo "iteration $i succeeded"