bidirectional links

Gemfile.lock

@@ -11,7 +11,7 @@ GEM
     ethon (0.12.0)
       ffi (>= 1.3.0)
     eventmachine (1.2.7)
-    ffi (1.14.2)
+    ffi (1.15.0)
     forwardable-extended (2.6.0)
     html-proofer (3.18.8)
       addressable (~> 2.3)
@@ -41,6 +41,9 @@ GEM
       terminal-table (~> 2.0)
     jekyll-feed (0.15.1)
       jekyll (>= 3.7, < 5.0)
+    jekyll-last-modified-at (1.3.0)
+      jekyll (>= 3.7, < 5.0)
+      posix-spawn (~> 0.3.9)
     jekyll-sass-converter (2.1.0)
       sassc (> 2.0.1, < 3.0)
     jekyll-watch (2.2.1)
@@ -56,13 +59,12 @@ GEM
     mercenary (0.4.0)
     nokogiri (1.11.1-x86_64-darwin)
       racc (~> 1.4)
-    nokogiri (1.11.1-x86_64-linux)
-      racc (~> 1.4)
     nokogumbo (2.0.4)
       nokogiri (~> 1.8, >= 1.8.4)
     parallel (1.20.1)
     pathutil (0.16.2)
       forwardable-extended (~> 2.6)
+    posix-spawn (0.3.15)
     public_suffix (4.0.6)
     racc (1.5.2)
     rainbow (3.0.0)
@@ -84,12 +86,12 @@ GEM
 
 PLATFORMS
   x86_64-darwin-19
-  x86_64-linux
 
 DEPENDENCIES
   html-proofer (~> 3.18)
   jekyll (~> 4.2.0)
   jekyll-feed (~> 0.12)
+  jekyll-last-modified-at (~> 1.3)
   rake (~> 13.0)
   tzinfo (~> 1.2)
   tzinfo-data