Bump scopt from 3.6.0 -> 3.7.0 (#877)

This bumps scopt from 3.6.0 to 3.7.0 to align with FIRRTL. FIRRTL
requires 3.7.0+ for added scopt methods that allow introspection
of options (e.g., examing the short options of a long option).
This bump avoids a compile-time warning due to the version
mistmatch.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>