Ensure file content is read as UTF-8

lib/propshaft/asset.rb

@@ -9,7 +9,7 @@ def initialize(path, logical_path:, version: nil)
   end
 
   def content
-    File.binread(path)
+    File.binread(path).force_encoding("UTF-8")
   end
 
   def content_type

test/fixtures/assets/first_path/utf-8.txt

@@ -0,0 +1 @@
+Ε

test/propshaft/asset_test.rb

@@ -51,6 +51,10 @@ class Propshaft::AssetTest < ActiveSupport::TestCase
     assert_equal asset.digest.object_id, asset.digest.object_id
   end
 
+  test "content with utf-8" do
+    assert_equal "Ε", find_asset("utf-8.txt").content
+  end
+
   private
     def find_asset(logical_path)
       root_path = Pathname.new("#{__dir__}/../fixtures/assets/first_path")