Minor table formating fix
Minor table formating fix

Table in "Lists, Nullable Lists, and Lists of Nulls" section was not properly formatted and GitHub did not render it correctly.
rmosolgo/graphql-ruby,nevesenin/graphql-ruby,rmosolgo/graphql-ruby,rmosolgo/graphql-ruby,nevesenin/graphql-ruby,nevesenin/graphql-ruby,rmosolgo/graphql-ruby,nevesenin/graphql-ruby