travis: use --verbose-log test option

Because we run the tests via "prove", the output from
"--verbose" may interfere with our TAP output. Using
"--verbose-log" solves this while letting us retain our
on-disk log.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

.travis.yml

@@ -29,7 +29,7 @@ env:
     - LINUX_GIT_LFS_VERSION="1.2.0"
     - DEFAULT_TEST_TARGET=prove
     - GIT_PROVE_OPTS="--timer --jobs 3 --state=failed,slow,save"
-    - GIT_TEST_OPTS="--verbose --tee"
+    - GIT_TEST_OPTS="--verbose-log"
     - GIT_TEST_CLONE_2GB=YesPlease
     # t9810 occasionally fails on Travis CI OS X
     # t9816 occasionally fails with "TAP out of sequence errors" on Travis CI OS X