Failed loading filenames with `+`

https://github.com/awslabs/aws-lambda-redshift-loader/blob/master/index.js#L785-L790

This line is replacing all `+` with ` ` (whitespace) which is problematic for filenames with `+`, e.g.:
Original filename in S3: `hello+world.csv`
Generated manifest: `hello world.csv`
Then Redshift will complain the key does not exist when trying to load the manifest.
I manually changed it to:
```
url: 's3://' + batchEntries[i],
```
and it worked fine for me.