Datatype of Number columns changed to String

Source table:

```
Partition key
scheduleId (Number)
Sort key
timestamp (Number)
```

Command:

```
docker run --rm -v $HOME/.aws:/root/.aws -it techgaun/dynamodb-copy-table:latest source dest
```

Destination table:

```
Partition key
scheduleId (String)
Sort key
timestamp (String)
```