Expose Resource#modified? as public

Can be useful when doing conditional saving of resources or similar
functionality

lib/passwordstate/resource.rb

@@ -151,6 +151,12 @@ module Passwordstate
       end
     end
 
+    def modified?(field = nil)
+      return modified.any? unless field
+
+      modified.include? field
+    end
+
     protected
 
     def api_path
@@ -162,10 +168,6 @@ module Passwordstate
       attribs.reject { |field| old[field] == attribs[field] }
     end
 
-    def modified?(field)
-      modified.include? field
-    end
-
     def old
       @old ||= attributes.dup
     end