Usage of Ruby's Safe Navigation Operator (&.) is causing issues when using Ruby versions < 2.3.0 #9

The respond_to_missing function in lib/ostruct.rb is causing issues when using versions of Ruby < 2.3.0

def respond_to_missing?(mid, include_private = false) # :nodoc:
    mname = mid.to_s.chomp("=").to_sym
    @table&.key?(mname) || super
end

Line 196 uses the &. (Safe Navigation Operator) which was introduced in Ruby 2.3.0.

If you want to use the Safe Navigation Operator then please specify the required_ruby_version property in the ostruct.gemspec file