[HOTFIX] downgrade breeze version to 0.7

breeze-0.8.1 causes dependency issues, as discussed in #940 .

Author: Xiangrui Meng <meng@databricks.com>

Closes #1718 from mengxr/revert-breeze and squashes the following commits:

99c4681 [Xiangrui Meng] downgrade breeze version to 0.7