diff --git a/docs/Gemfile b/docs/Gemfile
index fc892603..9e526abe 100644
--- a/docs/Gemfile
+++ b/docs/Gemfile
@@ -5,4 +5,4 @@ source "https://rubygems.org"
 
 # just do `bundle update` to get the latest version.
 
-gem 'github-pages'
+gem "github-pages"