Bump src/gnatsd

Bump apcera/gnatsd:
  Derek Collison:
     Merge pull request #51 from zrob/stale_subs_rebase ( Travis Success: https://travis-ci.org/apcera/gnatsd/builds/35701380 )
     Make sure to wait long enough ( Travis Success: https://travis-ci.org/apcera/gnatsd/builds/35699210 )
     Merge pull request #50 from apcera/test_cleanup ( Travis Failed: https://travis-ci.org/apcera/gnatsd/builds/35698989 )
     Fix log calls ( Travis Unknown )
     pedantic about over zealous GC for sockets ( Travis Unknown )
     rand contention TODO ( Travis Unknown )
     function closures ( Travis Unknown )
  Julian Friedman and Zach Robinson:
     No longer add subscriptions to router clients with no existing connection. ( Travis Unknown )