* Remove f-string, since it's not supported by Python 3.5 (#5330)
* Remove f-string, since it's not supported by Python 3.5
* Add Python 3.5 to CI, to ensure compatibility
* Remove duplicated matplotlib
* Show deprecation notice for Python 3.5
* Fix lint
* Fix lint
* Fix a unit test that mistook MINOR ver for PATCH ver
* Enforce only major version in JSON model schema
* Bump version to 1.1.0-SNAPSHOT
Currently `pip install xgboost` will raise traceback like this
```
Traceback (most recent call last):
File "<string>", line 20, in <module>
File "/tmp/pip-build-IAdqYE/xgboost/setup.py", line 20, in <module>
import xgboost
File "./xgboost/__init__.py", line 8, in <module>
from .core import DMatrix, Booster
File "./xgboost/core.py", line 12, in <module>
import numpy as np
ImportError: No module named numpy
```
We should avoid importing numpy in setup.py and let pip install numpy and scipy automatically.
That's what `install_requires` for.
