Suppress offences if rhs is block node in ConstantName cop

The cop is already ignoring non SCREAMING_SNAKE_CASE name constant
assignments when rhs is a send node.
This change adds block type to the types to ignore.

This fixes #432.
Merge pull request #433 from yujinakayama/fix-constant-assignment-with-block

Suppress offences if rhs is block node in ConstantName cop