Fix syntax errors of generated TypeScript code in ts-helper.js

[isac322]

#176 is very useful but I think it's generating a syntax error code.

Example:

import sequelize from 'sequelize';

should change to

import * as sequelize from 'sequelize';

Found in microsoft/TypeScript#3337.

[mention-bot]

@isac322, thanks for your PR! By analyzing the history of the files in this pull request, we identified @gsdnano to be a potential reviewer.

[durango]

Thanks! 👍