Fix go modules

Wow. This is fun. Sure is easy to get modules wrong when upgrading a v2+
project.

stdlib/opendb.go

@@ -7,7 +7,7 @@ import (
 	"database/sql"
 	"database/sql/driver"
 
-	"github.com/jackc/pgx"
+	"github.com/jackc/pgx/v4"
 )
 
 // OptionOpenDB options for configuring the driver when opening a new db pool.

stdlib/sql.go

@@ -83,8 +83,8 @@ import (
 	errors "golang.org/x/xerrors"
 
 	"github.com/jackc/pgconn"
-	"github.com/jackc/pgx"
-	"github.com/jackc/pgx/pgtype"
+	"github.com/jackc/pgx/v4"
+	"github.com/jackc/pgx/v4/pgtype"
 )
 
 // oids that map to intrinsic database/sql types. These will be allowed to be

stdlib/sql_test.go

@@ -12,10 +12,10 @@ import (
 	"time"
 
 	"github.com/jackc/pgconn"
-	"github.com/jackc/pgproto3"
-	"github.com/jackc/pgx"
-	"github.com/jackc/pgx/pgmock"
-	"github.com/jackc/pgx/stdlib"
+	"github.com/jackc/pgproto3/v2"
+	"github.com/jackc/pgx/v4"
+	"github.com/jackc/pgx/v4/pgmock"
+	"github.com/jackc/pgx/v4/stdlib"
 )
 
 func closeDB(t *testing.T, db *sql.DB) {

stdlib/stdlibutil110_test.go

@@ -6,8 +6,8 @@ import (
 	"database/sql"
 	"testing"
 
-	"github.com/jackc/pgx"
-	"github.com/jackc/pgx/stdlib"
+	"github.com/jackc/pgx/v4"
+	"github.com/jackc/pgx/v4/stdlib"
 )
 
 func openDB(t *testing.T) *sql.DB {