Go Modules Support

### Issue Summary
Is there any plans in the future to support go modules. As at the minute the import is marked as `incompatible` when using any version above v1 

for example the import should be renamed to have the major version suffixed: 
```go
github.com/sendgrid/sendgrid-go v3.5.0+incompatible => github.com/sendgrid/sendgrid-go/v3 v3.5.0 
```
