Add RoundTripper request clone changelog entry
* [documentation](https://godoc.org/github.com/newrelic/go-agent/_integrations/nrlambda)
* [working example](_integrations/nrlambda/example/main.go)
+### Bug Fixes
+
+* The [http.RoundTripper](https://golang.org/pkg/net/http/#RoundTripper) returned
+ by [NewRoundTripper](https://godoc.org/github.com/newrelic/go-agent#NewRoundTripper)
+ no longer modifies the request. Our thanks to @jlordiales for the contribution.
+
## 2.6.0
### New Features
