Bump version to 1.5.1

Release 1.5.0. (dmlc#7317)

Change version to 1.5.0. (dmlc#7258)

Make 1.4.2 patch release. (dmlc#6962)

Release 1.4.1 (dmlc#6874)

Release 1.4.0

Bump release version to 1.3.3. (dmlc#6624)

 Release patch release 1.3.2

Release patch release 1.3.1 (dmlc#6543)

Fix dask ip resolution. (dmlc#6475)

This adopts the solution used in dask/dask-xgboost#40 which employs the get_host_ip from dmlc-core tracker.