Let http.url tag adhere to the semantic standard

[W3D3]

I noticed when using this library that the http.url tag is always just filled out with the path after the base URL. According to the Semantic Convention of OpenTracing (and also the newer one from OpenTelemetry) the http.url tag has to be filled with the full URI:

Excerpt below taken from https://github.com/opentracing/specification/blob/master/semantic_conventions.md

http.url	string	URL of the request being handled in this segment of the trace, in standard URI format. E.g., "https://domain.net/path/to?resource=here"

This PR changes this behavior by feeding the concatenated full URL to the http.url tag.