look in /usr/local/bin/ before /usr/local/sbin/

according to [heir(7)](https://man.freebsd.org/cgi/hier) /sbin/ is for
binaries fundamental to single-user and multi-user environments, which
fdb is definitely not.
diff --git a/src/erlfdb_util.erl b/src/erlfdb_util.erl
index 5a6224b..4dbbc7d 100644
--- a/src/erlfdb_util.erl
+++ b/src/erlfdb_util.erl
@@ -177,6 +177,7 @@
         undefined ->
             [
                 <<"/usr/sbin/fdbserver">>,
+                <<"/usr/local/bin/fdbserver">>,
                 <<"/usr/local/sbin/fdbserver">>,
                 <<"/usr/local/libexec/fdbserver">>
             ];