Travis test mac_zones failure

[johnfxgalea]

Seems like we have a non-flaky test failure on Travis for Mac OS.

61: ~~Dr.M~~ Dr. Memory version 2.3.169

61: ~~Dr.M~~ WARNING: Dr. Memory for Mac is Beta software.  Please report any

61: ~~Dr.M~~ problems encountered to http://drmemory.org/issues.

61: <ran out of stolen fd space>

61: <curiosity: rex.w on OPSZ_6_irex10_short4!>

61: <(1+x) Handling our fault in a TRY at 0x0000000102b6f296>

61: <Application /Users/travis/build/DynamoRIO/drmemory/build_drmemory-dbg-64/tests/mac_zones (94825).  Dr. Memory internal crash at PC 0x0000000102e1dca4.  Please report this at http://drmemory.org/issues.  Program aborted.

Details: https://travis-ci.com/github/DynamoRIO/drmemory/jobs/382382046