Instrument FileScraper read errors rather than use puts

lib/docs/core/scrapers/file_scraper.rb

@@ -41,7 +41,7 @@ module Docs
     def read_file(path)
       File.read(path)
     rescue
-      puts "Failed to open file: #{path}"
+      instrument 'warn.doc', msg: "Failed to open file: #{path}"
       nil
     end
   end

lib/docs/subscribers/doc_subscriber.rb

@@ -26,6 +26,10 @@ module Docs
       log event.payload[:msg]
     end
 
+    def warn(event)
+      log "ERROR: #{event.payload[:msg]}"
+    end
+
     def error(event)
       exception = event.payload[:exception]
       log "ERROR:"