Fix OTLP GRPC example (#856)

Author: erdemkose

examples/metrics/features/exporters/otlp_grpc.php

@@ -7,6 +7,7 @@
 use OpenTelemetry\API\Common\Signal\Signals;
 use OpenTelemetry\Contrib\Grpc\GrpcTransportFactory;
 use OpenTelemetry\Contrib\Otlp\MetricExporter;
+use OpenTelemetry\Contrib\Otlp\OtlpUtil;
 use OpenTelemetry\Example\ExampleMetricsGenerator;
 use OpenTelemetry\SDK\Common\Time\ClockFactory;
 use OpenTelemetry\SDK\Metrics\MetricReader\ExportingReader;
@@ -17,7 +18,7 @@
 
 $reader = new ExportingReader(
     new MetricExporter(
-        (new GrpcTransportFactory())->withSignal(Signals::METRICS)->create('http://collector:4317')
+        (new GrpcTransportFactory())->create('http://collector:4317' . OtlpUtil::method(Signals::METRICS))
     ),
     $clock
 );