HOTFIX: Remove generated-mima-excludes file after runing MIMA.

This has been causing some false failures on PR's that don't merge
correctly.

Author: Patrick Wendell <pwendell@gmail.com>

Closes #971 from pwendell/mima and squashes the following commits:

1dc80aa [Patrick Wendell] HOTFIX: Remove generated-mima-excludes file after runing MIMA.
sbt 0.13.X should be using sbt-assembly 0.11.X

https://github.com/sbt/sbt-assembly/blob/master/README.md

Author: Kalpit Shah <shahkalpit84@gmail.com>

Closes #555 from kalpit/upgrade/sbtassembly and squashes the following commits:

1fa7324 [Kalpit Shah] sbt 0.13.X should be using sbt-assembly 0.11.X
Remove compile-scoped junit dependency.

This avoids having junit classes showing up in the assembly jar.
I verified that only test classes in the jtransforms package
use junit.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #794 from vanzin/junit-dep-exclusion and squashes the following commits:

274e1c2 [Marcelo Vanzin] Remove junit from assembly in sbt build also.
ad950be [Marcelo Vanzin] Remove compile-scoped junit dependency.