UseSqlServer is not defined in DbContextOptionBuilder

I am trying to configure entity framework 7 in my console application.

However , I noticed that "UseSqlServer" is not defined in DbContextOptionBuilder

Here is the code

public class LetsBreakITContext : DbContext
    {
        public DbSet<Book> Books { get; set; }
        public DbSet<Country> Countries { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=EFGetStarted.ConsoleApp.NewDb;Trusted_Connection=True;");
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            //country
            modelBuilder.Entity<Country>(c =>
           {
               c.HasKey(e => e.CountryId);
               c.Property(e => e.CountryId).ValueGeneratedOnAdd();
               c.Property(e => e.CountryId).IsRequired();
               c.Property(e => e.Name).IsRequired();
           });
            //Book
            modelBuilder.Entity<Book>(l =>
            {
                l.HasKey(e => e.BookId);
                l.Property(e => e.BookId).ValueGeneratedOnAdd();
                l.Property(e => e.CountryId).IsRequired();
                l.Property(e => e.Name).IsRequired();
            });
        }
    }

I added EF 7 using Nuget "install-package entityframework.commands -pre"

I am using the sample code from Microsoft's EF 7 documentation Not sure what I am missing here.

-Alan-