Switch bazel version to 0.29.1
Switch bazel version to 0.29.1

We previously updated to 1.0.0rc2 which isn't released yet to
avoid a security issue. The security issue has been cherry-picked
back to 0.29 and released in 0.29.1:

  https://github.com/bazelbuild/bazel/commit/1b771ec1fc8f859c64c3c14a57c53bf0aa2ecb51

Since 0.29.1 is released, update our requirement to that, so that
people can continue to use released things.

Change-Id: Ib48fdbb61bc94a5e78e81e485a5e1d550445a5a5

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