Allow remove_derivatives to receive string arg normalized to symbol

lib/shrine/plugins/kithe_persisted_derivatives.rb

@@ -134,6 +134,10 @@ def create_persisted_derivatives(*args, storage: nil, allow_other_changes: false
         def remove_persisted_derivatives(*paths, **options)
           return if paths.empty?
 
+          # Shrine does weird things if we pass in Strings, let's save ourselves
+          # the terrible debugging on that mistake, and noramlize to symbols
+          paths = paths.collect(&:to_sym)
+
           other_changes_allowed = !!options.delete(:allow_other_changes)
           if record && !other_changes_allowed && record.changed?
             raise TypeError.new("Can't safely add_persisted_derivatives on model with unsaved changes. Pass `allow_other_changes: true` to force.")

spec/shrine/kithe_persisted_derivatives_spec.rb

@@ -351,6 +351,14 @@ def sample_deriv_file!(path = Kithe::Engine.root.join("spec/test_support/images/
       expect(removed.first.exists?).to be(false)
     end
 
+    it "can remove string argument normalized to symbol" do
+      removed = asset.file_attacher.remove_persisted_derivatives("sample1")
+
+      expect(asset.file_derivatives.keys).to eq([:sample2])
+      expect(removed.first).to be_kind_of(Shrine::UploadedFile)
+      expect(removed.first.exists?).to be false
+    end
+
     describe "if someone else removed first" do
       before do
         another_copy = asset.class.find(asset.id)