fixed callback topic send error bug.

src/DotNetCore.CAP.MySql/CapPublisher.cs

@@ -30,11 +30,11 @@ namespace DotNetCore.CAP.MySql
             _dbContext = (DbContext) ServiceProvider.GetService(_options.DbContextType);
         }
 
-        public Task PublishAsync(CapPublishedMessage message)
+        public async Task PublishAsync(CapPublishedMessage message)
         {
             using (var conn = new MySqlConnection(_options.ConnectionString))
             {
-                return conn.ExecuteAsync(PrepareSql(), message);
+                await conn.ExecuteAsync(PrepareSql(), message);
             }
         }
 

src/DotNetCore.CAP.PostgreSql/CapPublisher.cs

@@ -32,11 +32,11 @@ namespace DotNetCore.CAP.PostgreSql
             }
         }
          
-        public Task PublishAsync(CapPublishedMessage message)
+        public async Task PublishAsync(CapPublishedMessage message)
         {
             using (var conn = new NpgsqlConnection(_options.ConnectionString))
             {
-                return conn.ExecuteAsync(PrepareSql(), message);
+                await conn.ExecuteAsync(PrepareSql(), message);
             }
         }
 

src/DotNetCore.CAP.SqlServer/CapPublisher.cs

@@ -28,14 +28,14 @@ namespace DotNetCore.CAP.SqlServer
             if (_options.DbContextType == null) return;
 
             IsUsingEF = true;
-            _dbContext = (DbContext) ServiceProvider.GetService(_options.DbContextType);
+            _dbContext = (DbContext)ServiceProvider.GetService(_options.DbContextType);
         }
 
-        public Task PublishAsync(CapPublishedMessage message)
+        public async Task PublishAsync(CapPublishedMessage message)
         {
             using (var conn = new SqlConnection(_options.ConnectionString))
             {
-               return conn.ExecuteAsync(PrepareSql(), message);
+               await conn.ExecuteAsync(PrepareSql(), message);
             }
         }