Allow selecting image type via Regexp

For example, SVG images might be of type "image/svg" or "image/svg+xml"

spec/manifique/metadata_spec.rb

@@ -68,6 +68,16 @@ RSpec.describe Manifique::Metadata do
         icon = metadata.select_icon(type: "image/png")
         expect(icon["sizes"]).to eq("512x512")
       end
+
+      it "matches strings exactly" do
+        icon = metadata.select_icon(type: "image/svg")
+        expect(icon["type"]).to eq("image/svg")
+      end
+
+      it "works with a regex" do
+        icon = metadata.select_icon(type: /image\/svg/)
+        expect(icon["type"]).to eq("image/svg+xml")
+      end
     end
 
     describe "by size" do