Update tool/rbinstall.rb

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: hsbt

tool/rbinstall.rb

@@ -881,7 +881,7 @@ def load_gemspec(file, base = nil, files: nil)
 
   spec = eval(code, binding, file)
   # for out-of-place build
-  collected_files = files ? files.map{|f| File.exist?(File.join(base || ".", f)) ? f : "lib/#{f}" }.select{|f| f.end_with?(".rb")} : []
+  collected_files = files ? files.map {|f| File.exist?(File.join(base || ".", f)) ? f : "lib/#{f}" }.select {|f| f.end_with?(".rb")} : []
   spec.files = spec.files.concat(collected_files).uniq
   unless Gem::Specification === spec
     raise TypeError, "[#{file}] isn't a Gem::Specification (#{spec.class} instead)."