Use interpolation instead of concatenation

app/controllers/metrics_controller.rb

@@ -14,7 +14,7 @@ class MetricsController < ActionController::Base
 
   def metrics
     metrics_text = Prometheus::Client::Formats::Text.marshal_multiprocess(multiprocess_metrics_path)
-    response = health_metrics_text + "\n" + metrics_text
+    response = "#{health_metrics_text}\n#{metrics_text}"
 
     render text: response, content_type: 'text/plain; version=0.0.4'
   end
@@ -32,15 +32,15 @@ class MetricsController < ActionController::Base
   def health_metrics_text
     results = CHECKS.flat_map(&:metrics)
 
-    types = results.map(&:name)
-              .uniq
-              .map { |metric_name| "# TYPE #{metric_name} gauge" }
+    types = results.map(&:name).uniq.map { |metric_name| "# TYPE #{metric_name} gauge" }
     metrics = results.map(&method(:metric_to_prom_line))
+
     types.concat(metrics).join("\n")
   end
 
   def metric_to_prom_line(metric)
     labels = metric.labels&.map { |key, value| "#{key}=\"#{value}\"" }&.join(',') || ''
+
     if labels.empty?
       "#{metric.name} #{metric.value}"
     else