Switch upload_revision.py to new git-cl try -B syntax

TBR=ehmaldonado

Bug: 1018293
Change-Id: Id6ccd9427ccc9444f2f411eab98ce76a8c98e34e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1943131Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720141}

tools/clang/scripts/upload_revision.py

@@ -100,7 +100,7 @@ def main():
       old_rev_string, rev_string, commit_message)])
 
   Git(["cl", "upload", "-f", "--bypass-hooks"])
-  Git(["cl", "try", "-B", "luci.chromium.try",
+  Git(["cl", "try", "-B", "chromium/try",
        "-b", "linux_upload_clang",
        "-b", "mac_upload_clang",
        "-b", "win_upload_clang",