Make checklicenses ignore tools\telemetry\third_party\gs_util.

telemetry downloads gsutil sometimes there when its running tests. This isn't shipped to users.

R=thestig@chromium.org

Review URL: https://codereview.chromium.org/672513002

Cr-Commit-Position: refs/heads/master@{#300567}

tools/checklicenses/checklicenses.py

@@ -398,6 +398,10 @@ PATH_SPECIFIC_WHITELISTED_LICENSES = {
     'tools/symsrc/pefile.py': [
         'UNKNOWN',
     ],
+    # Not shipped, downloaded on trybots sometimes.
+    'tools/telemetry/third_party/gsutil': [
+        'UNKNOWN',
+    ],
     'tools/telemetry/third_party/pyserial': [
         # https://sourceforge.net/p/pyserial/feature-requests/35/
         'UNKNOWN',