Update specification/trace/api.md

Co-authored-by: Armin Ruech <armin.ruech@gmail.com>

specification/trace/api.md

@@ -227,7 +227,7 @@ hypothetical account information:
 The `Span`'s start and end timestamps reflect the elapsed real time of the
 operation.
 
-For example, an http server span should start right when the request has begun being handled by the server, and end when the response has been completely sent.
+For example, an HTTP server span SHOULD start right when the server starts handling the request, and end when the response has been completely sent.
 This would include the following, if they are present in that particular
 request-response cycle: