title: update Migration Command Fails for ConfigurationDbContext and PersistentGrantDbContext
body: <p>I have  been trying to get IdentityServer4 version 1.5.2 to work for a few days now without success. I am using VS2017
  My Entity classes,DataContexts, repositories and migrations are resident in a .Net Standard Library (1.6). So far so good except when I run update-migration command for "PersistenGrantDbContext" and "ConfigurationDbCOntext". I get the error message </p>
  
  <pre><code>Could not load file or assembly 'System.Data.SqlClient, Version=4.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'. The system cannot find the file specified.
  </code></pre>
  
  <p>The datacontext classes that i created myself dont seem to have this problem after implementing "IDbContextFactory" interface 
  Here I have the implementation for the two culprits</p>
  
  <pre><code>public class TemporaryDbContextFactoryScopes : IDbContextFactory&lt;PersistedGrantDbContext&gt;
  {
      public PersistedGrantDbContext Create(DbContextFactoryOptions options)
      {
          var builder = new DbContextOptionsBuilder&lt;PersistedGrantDbContext&gt;();
          builder.UseSqlServer("Server=-------;Database=-----------;Trusted_Connection=True;MultipleActiveResultSets=true",
              optionsBuilder =&gt; optionsBuilder.MigrationsAssembly(typeof(UserDbContext).GetTypeInfo().Assembly.GetName().Name));
          return new PersistedGrantDbContext(builder.Options, new OperationalStoreOptions());
      }
  }
  
  public class TemporaryDbContextFactoryOperational : IDbContextFactory&lt;ConfigurationDbContext&gt;
  {
      public ConfigurationDbContext Create(DbContextFactoryOptions options)
      {
          var builder = new DbContextOptionsBuilder&lt;ConfigurationDbContext&gt;();
          builder.UseSqlServer("Server=---------;Database=--------;Trusted_Connection=True;MultipleActiveResultSets=true",
              optionsBuilder =&gt; optionsBuilder.MigrationsAssembly(typeof(UserDbContext).GetTypeInfo().Assembly.GetName().Name));
  
          return new ConfigurationDbContext(builder.Options, new ConfigurationStoreOptions());
      }
  }
  </code></pre>
  
  <p>I have installed the latest version of System.Data.SqlClient still not working</p>