Add attr_reader to Wraith::Spider to fix error "undefined local variable or method `wraith'"
Add attr_reader to Wraith::Spider to fix error "undefined local variable or method `wraith'"

resolves #401, #422

BBC-News/wraith,BBC-News/wraith,saulirajala/wraith,saulirajala/wraith,BBC-News/wraith,saulirajala/wraith