Update bazel-toolchains to rev 3 via SR 765219
    
    https://build.opensuse.org/request/show/765219
    by user dimstar_suse
    - Update to version 2.0.0:
      * Toolchain configs for marketplace.gcr.io/google/rbe-ubuntu16-04, Bazel 2.0.0 (2019/12/20) (#790)
      * Project import generated by Copybara. (#782)
      * Release commit list update (#784)
      * Toolchain configs for marketplace.gcr.io/google/rbe-ubuntu16-04, Bazel 1.2.1 (2019/12/11) (#783)
      * Release commit list update (#781)
      * Toolchain configs for marketplace.gcr.io/google/rbe-ubuntu16-04, Bazel 1.2.1 (2019/12/09) (#780)
      * Project import generated by Copybara. (#776)
      * Release commit list update (#779)
    
    - Update to version 1.2.2:
      * Toolchain configs for marketplace.gcr.io/google/rbe-ubuntu16-04, Bazel 1.2.1 (2019/12/04) (#777)
      * Disable failing Abseil test (#778)
      * Move tests that use 'docker' to GCB (#771)
      * Release commit list update (#775)
      * To