fix protocol priority (#71)

*Issue #, if available:*

This PR fix the SMP exporter transport protocol as priority:

1. OTEL_EXPORTER_OTLP_METRICS_PROTOCOL
2. OTEL_EXPORTER_OTLP_PROTOCOL


By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice.

Author: wangzlei

aws-opentelemetry-distro/src/amazon/opentelemetry/distro/aws_opentelemetry_configurator.py

@@ -228,7 +228,7 @@ def __new__(cls, *args, **kwargs):
     # pylint: disable=no-self-use
     def create_exporter(self):
         protocol = os.environ.get(
-            OTEL_EXPORTER_OTLP_PROTOCOL, os.environ.get(OTEL_EXPORTER_OTLP_METRICS_PROTOCOL, "grpc")
+            OTEL_EXPORTER_OTLP_METRICS_PROTOCOL, os.environ.get(OTEL_EXPORTER_OTLP_PROTOCOL, "grpc")
         )
         _logger.debug("AppSignals export protocol: %s", protocol)