Fix patch command invocation

It has been broken since e5fa660 :(

Author: kateinoigakukun

lib/ruby_wasm/build/product/ruby_source.rb

@@ -80,7 +80,7 @@ def fetch(executor)
         raise "unknown source type: #{@params[:type]}"
       end
       (@params[:patches] || []).each do |patch_path|
-        executor.system "patch", "-p1", patch_path, chdir: src_dir
+        executor.system "patch", "-p1", "-i", patch_path, chdir: src_dir
       end
     end