Allow setting file permissions with create_file

Previously, to restrict the permissions of a file created using
create_file, chmod could be called right after. However, that leaves a
short amount of time between when the file is first created and when the
permissions are updated where another user could read the file.

This commit enables passing file permissions to create_file so that
permissions can be set when the file is created.

lib/thor/actions/create_file.rb

@@ -60,7 +60,7 @@ def invoke!
         invoke_with_conflict_check do
           require "fileutils"
           FileUtils.mkdir_p(File.dirname(destination))
-          File.open(destination, "wb") { |f| f.write render }
+          File.open(destination, "wb", config[:perm]) { |f| f.write render }
         end
         given_destination
       end

spec/actions/create_file_spec.rb

@@ -33,6 +33,14 @@ def silence!
       expect(File.exist?(File.join(destination_root, "doc/config.rb"))).to be true
     end
 
+    it "allows setting file permissions" do
+      create_file("config/private.key", :perm => 0o600)
+      invoke!
+
+      stat = File.stat(File.join(destination_root, "config/private.key"))
+      expect(stat.mode.to_s(8)).to eq "100600"
+    end
+
     it "does not create a file if pretending" do
       create_file("doc/config.rb", {}, :pretend => true)
       invoke!