Log Message:
devel/ruby-shoulda-matchers: update to 3.1.3

Update ruby-shoulda-matchers to 3.1.3.
pkgsrc change: Do not restrict to Rails to 4.2.

# 3.1.3

### Improvements

* Update `BigDecimal.new()` to use `BigDecimal()` and avoid deprecation warnings
  in Ruby 2.6.