In builder config, change "is_try_bot" -> "is_try_builder".

In http://crrev.cm/2019463003, I accidentally used is_try_bot in one
place and is_try_builder in the rest of the places. This CL makes the
usage consistent so that those three builders are actually considered
try bots (for the purposes of rebaseline-from-try-bots).

Review-Url: https://codereview.chromium.org/2135393002
Cr-Commit-Position: refs/heads/master@{#404717}
1 file changed