fix: missing export for VirtualizedMessageList type (#691)

Author: Amin Mahboubi

types/index.d.ts

@@ -1342,6 +1342,7 @@ export class Channel extends React.PureComponent<ChannelProps, any> {}
 export class Avatar extends React.PureComponent<AvatarProps, any> {}
 export class Message extends React.PureComponent<MessageComponentProps, any> {}
 export class MessageList extends React.PureComponent<MessageListProps, any> {}
+export const VirtualizedMessageList: React.FC<VirtualizedMessageListProps>;
 export const ChannelHeader: React.FC<ChannelHeaderProps>;
 export class MessageInput extends React.PureComponent<MessageInputProps, any> {}
 export class MessageInputLarge extends React.PureComponent<