Fixed asp.net core 2.0 startup error about issue #44 of MySql and PostgreSql (#51)

Fixed asp.net core 2.0 startup error about issue #44 of MySql and PostgreSql

src/DotNetCore.CAP.MySql/CAP.MySqlCapOptionsExtension.cs

@@ -31,9 +31,13 @@ namespace DotNetCore.CAP
             {
                 services.AddSingleton(x =>
                 {
-                    var dbContext = (DbContext)x.GetService(mysqlOptions.DbContextType);
-                    mysqlOptions.ConnectionString = dbContext.Database.GetDbConnection().ConnectionString;
-                    return mysqlOptions;
+                    using (var scope = x.CreateScope())
+                    {
+                        var provider = scope.ServiceProvider;
+                        var dbContext = (DbContext)provider.GetService(mysqlOptions.DbContextType);
+                        mysqlOptions.ConnectionString = dbContext.Database.GetDbConnection().ConnectionString;
+                        return mysqlOptions;
+                    }
                 });
             }
             else

src/DotNetCore.CAP.PostgreSql/CAP.PostgreSqlCapOptionsExtension.cs

@@ -31,9 +31,13 @@ namespace DotNetCore.CAP
             {
                 services.AddSingleton(x =>
                 {
-                    var dbContext = (DbContext)x.GetService(postgreSqlOptions.DbContextType);
-                    postgreSqlOptions.ConnectionString = dbContext.Database.GetDbConnection().ConnectionString;
-                    return postgreSqlOptions;
+                    using (var scope = x.CreateScope())
+                    {
+                        var provider = scope.ServiceProvider;
+                        var dbContext = (DbContext)provider.GetService(postgreSqlOptions.DbContextType);
+                        postgreSqlOptions.ConnectionString = dbContext.Database.GetDbConnection().ConnectionString;
+                        return postgreSqlOptions;
+                    }
                 });
             }
             else