Improve the string maipulation

String manipulation improved and made simplestic with .join method:
Original: [here](https://github.com/gitdagray/csv-to-sql-insert/blob/main/src/index.ts#L40)
Improved: [here](https://github.com/qurashi-aqeel/csv-to-sql-insert/blob/qurashi-akeel/src/index.ts#L42)