chore: Update require_relative order

Since we're using an inline gemfile, call require_relative after the
grpc gem is available to avoid 'cannot load such file' errors.

Author: kaylareopelle

instrumentation/grpc/example/trace_demonstration.rb

@@ -1,6 +1,3 @@
-require_relative './proto/example_api_services_pb'
-require_relative './example_impl'
-
 require 'bundler/inline'
 
 gemfile do
@@ -12,6 +9,9 @@
   gem 'opentelemetry-sdk'
 end
 
+require_relative 'proto/example_api_services_pb'
+require_relative 'example_impl'
+
 ENV['OTEL_TRACES_EXPORTER'] = 'console'
 OpenTelemetry::SDK.configure do |c|
   c.use 'OpenTelemetry::Instrumentation::Grpc'