FIX: S3 rake task can ignore yarn.lock

lib/tasks/s3.rake

@@ -71,11 +71,8 @@ def assets
   manifest.assets.each do |_, path|
     fullpath = (Rails.root + "public/assets/#{path}").to_s
 
-    mime = MiniMime.lookup_by_filename(fullpath)
-    if mime.nil?
-      STDERR.puts "ERROR: could not determine mime type for #{fullpath}"
-    end
-
+    # Ignore files we can't find the mime type of, like yarn.lock
+    if mime = MiniMime.lookup_by_filename(fullpath)
       content_type = mime.content_type
 
       asset_path = "assets/#{path}"
@@ -94,6 +91,8 @@ def assets
       end
     end
 
+  end
+
   results
 end