style: format code with Go fmt and Gofumpt

This commit fixes the style issues introduced in 5a781c8 according to the output
from Go fmt and Gofumpt.

Details: #1

otel.go

@@ -62,8 +62,8 @@ func RegisterWithConfig(ctx context.Context, cfg *config.Config) (func(), error)
 
 // RegisterGlobalInstance creates the instance that will be used to report metrics and traces
 func RegisterGlobalInstance(ctx context.Context, me map[string]exporter.MetricReader, te map[string]exporter.SpanExporter,
-	metricReportingPeriod int, traceSampleRate float64, serviceName string) (func(), error) {
-
+	metricReportingPeriod int, traceSampleRate float64, serviceName string,
+) (func(), error) {
 	shutdownFn := func() {}
 	prop := propagation.NewCompositeTextMapPropagator(
 		propagation.TraceContext{},