Update xgboost version to 0.80

[ardunn]

Pip installations of xgboost 0.72 on windows platforms are troublesome.

[computron]

closed via 63a4df9

I think it took less time to close this issue than it probably did to open it?

[ardunn]

@computron thx

wasn't sure if anything would break. the circleci tests are not complete unless you run the "intensive" tests (/run_intensive.sh). i will run them now and see if all is good

[ardunn]

update: all is well