Log Message:
misc/ruby-slop: update to 4.8.0

Update ruby-slop to 4.8.0.

v4.8.0 (2020-01-17)
-------------------

Features:
  * Add support for prefixing integer values with `+` character
  [#243](https://github.com/leejarvis/slop/pull/243) (Juha Ylitalo)
  * Add support for parsing floats with scientific notation
  [#250](https://github.com/leejarvis/slop/pull/250) (Hansuk Hong)

Maintenance:
  * Add 2.7.0 to CI and fix warnings
  [#248](https://github.com/leejarvis/slop/pull/248) (Juha Ylitalo, Andrew Kane)