diff --git a/Gemfile.lock b/Gemfile.lock
old mode 100755
new mode 100644
index 983d617..7ea86d5
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -51,6 +51,8 @@ GEM
       sassc (> 2.0.1, < 3.0)
     jekyll-seo-tag (2.6.1)
       jekyll (>= 3.3, < 5.0)
+    jekyll-sitemap (1.4.0)
+      jekyll (>= 3.7, < 5.0)
     jekyll-toc (0.13.1)
       jekyll (>= 3.7)
       nokogiri (~> 1.9)
@@ -59,7 +61,8 @@ GEM
       listen (~> 3.0)
     katex (0.6.0)
       execjs (~> 2.7)
-    kramdown (2.1.0)
+    kramdown (2.3.1)
+      rexml
     kramdown-math-katex (1.0.1)
       katex (~> 0.4)
       kramdown (~> 2.0)
@@ -89,6 +92,7 @@ GEM
     rb-fsevent (0.10.3)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
+    rexml (3.2.4)
     rouge (3.16.0)
     rubyzip (2.2.0)
     safe_yaml (1.0.5)
@@ -120,6 +124,7 @@ DEPENDENCIES
   jekyll-relative-links
   jekyll-remote-theme
   jekyll-seo-tag
+  jekyll-sitemap
   jekyll-toc
   jekyll-twitter-plugin
   kramdown-math-katex