Upgrade gocql to 1.15.3 (#343)

gocql 1.15.3 brings new APIs for `gocql.Batch` and `gocql.Query`:
- `SetRequestTimeout`
- `GetRequestTimeout`

So, this change adds relative APIs to the `gocqlx.Batch` and `gocqlx.Queryx`.

batchx.go

@@ -3,6 +3,8 @@ package gocqlx
 import (
 	"context"
 	"fmt"
+	"time"
+
 	"github.com/gocql/gocql"
 )
 
@@ -34,6 +36,19 @@ func (s *Session) ContextBatch(ctx context.Context, bt gocql.BatchType) *Batch {
 	}
 }
 
+// GetRequestTimeout returns time driver waits for single server response
+// This timeout is applied to preparing statement request and for query execution requests
+func (b *Batch) GetRequestTimeout() time.Duration {
+	return b.Batch.GetRequestTimeout()
+}
+
+// SetRequestTimeout sets time driver waits for server to respond
+// This timeout is applied to preparing statement request and for query execution requests
+func (b *Batch) SetRequestTimeout(timeout time.Duration) *Batch {
+	b.Batch.SetRequestTimeout(timeout)
+	return b
+}
+
 // SetHostID allows to define the host the query should be executed against. If the
 // host was filtered or otherwise unavailable, then the query will error. If an empty
 // string is sent, the default behavior, using the configured HostSelectionPolicy will