Fixes on TransferEncoding and Trimming bug

On the last code, the TransferEncoding was commented out. I uncomment it and leave the default value to be Base64 which is the normal behavior.

The trimming bug on payload for SendGrid was fixed applying a Trim() before the workarounds. Otherwise, the hack was adding and extra closing bracket ']' when the payload ended with spaces and deserialization was failing.

Hope these changes can get updated to Nuget soon.