adds missing comma to opentelemetery_exporter config example (#87)

Author: krankin

examples/basic_phoenix_ecto/config/runtime.exs

@@ -86,7 +86,7 @@ if config_env() == :prod do
 
     # Example configuration for Lightstep.com, for more refers to:
     # https://github.com/open-telemetry/opentelemetry-erlang/tree/main/apps/opentelemetry_exporter#application-environment
-    # config :opentelemetry_exporter
+    # config :opentelemetry_exporter,
     #   # You can also configure the compression type for exporting traces.
     #   oltp_traces_compression: :gzip,
     #   otlp_traces_endpoint: "https://ingest.lightstep.com:443/traces/otlp/v0.9",