Skip pass actions if no test name is present (#8)

Go test json may produce output like:

{"Time":"2021-10-07T15:05:01.541387-05:00","Action":"pass","Package":"github.com/example/package","Elapsed":0.023}

Instead of returning from the goroutine and hanging go-test-trace, just
skip it.

README.md

@@ -62,14 +62,14 @@ $ go test -v ./example | go-test-trace -stdin
 You can export to any collector by using the endpoint flag:
 
 ```
-$ go-test-trace ./example -endpoint=my-otel-collector.io:9090
+$ go-test-trace -endpoint=my-otel-collector.io:9090 ./example
 ```
 
 You can make the go-test-trace to participate into an existing
 trace with the traceparent flag.
 
 ```
-$ go-test-trace ./example -traceparent=00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01
+$ go-test-trace -traceparent=00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01 ./example
 ```
 
 ## Running the collector

main.go

@@ -139,6 +139,9 @@ func trace(args []string) error {
 					startTime: data.Time,
 				}
 			case "pass", "fail", "skip":
+				if data.Test == "" {
+					continue
+				}
 				spanData, ok := collectedSpans[data.Test]
 				if !ok {
 					return // should never happen