build: enable race detector in Travis tests
build: enable race detector in Travis tests

Change-Id: Ia578b8978f1eab77b4113c1281c879550d68d49d
Reviewed-on: https://upspin-review.googlesource.com/8403
Reviewed-by: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>

upspin/upspin,upspin/upspin