title: Unable to await SetStringAsync in IDistributedCache
body: <p>I am using .NET Core 2.0 with Microsoft.Extensions.Caching.Redis 2.0. Why is IDistributedCache.SetStringAsync not actually marked as async, and therefore not awaitable?</p>
  
  <pre><code>        var services = new ServiceCollection();
          services.AddDistributedRedisCache(options =&gt;
          {
              options.Configuration = "127.0.0.1";
              options.InstanceName = "master";
          });
  
          var provider = services.BuildServiceProvider();
  
          var cache = provider.GetService&lt;IDistributedCache&gt;();
  
          // Does not compile
          await cache.SetStringAsync("mykey", "myvalue");
  </code></pre>