title: EF Core 2.1 - Verify if database exists dont work after update
body: <p>This code worked perfectly before update NPGSQL from 2.0 to 2.1</p>
  
  <pre><code>public static void EnsurePopulated(IApplicationBuilder app)
  {
      CoreDatabaseContext context = app.ApplicationServices.GetRequiredService&lt;CoreDatabaseContext&gt;();
      bool databaseExists  = (context.Database.GetService&lt;IDatabaseCreator&gt;() as RelationalDatabaseCreator).Exists();
  
      //Don't work too
      //bool databaseExists  = context.Database.EnsureCreated(); 
  }
  </code></pre>
  
  <p>After update i got the error:</p>
  
  <blockquote>
    <p>System.MissingMethodException: 'Method not found:
    'Microsoft.EntityFrameworkCore.DbContextOptionsBuilder
    Microsoft.EntityFrameworkCore.NpgsqlDbContextOptionsExtensions.UseNpgsql(Microsoft.EntityFrameworkCore.DbContextOptionsBuilder,
    System.String,
    System.Action`1)'.'</p>
  </blockquote>
  
  <p>VS2017 15.7.0
  .NET 4.7.2
  Npgsql.EntityFrameworkCore.PostgreSQL 2.1
  .NET Core 2.1.300</p>