diff --git a/Gemfile.lock b/Gemfile.lock
index 0ca273a..c1451d3 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -31,8 +31,8 @@ GEM
     ethon (0.12.0)
       ffi (>= 1.3.0)
     ffi (1.14.0)
-    gepub (1.0.12)
-      nokogiri (>= 1.8.2, < 1.11)
+    gepub (1.0.15)
+      nokogiri (>= 1.8.2, < 2.0)
       rubyzip (> 1.1.1, < 2.4)
     hashery (2.1.2)
     html-proofer (3.18.2)
@@ -48,11 +48,12 @@ GEM
     mime-types (3.3.1)
       mime-types-data (~> 3.2015)
     mime-types-data (3.2020.1104)
-    mini_portile2 (2.4.0)
     multi_json (1.15.0)
-    nokogiri (1.10.10)
-      mini_portile2 (~> 2.4.0)
-    nokogumbo (2.0.4)
+    nokogiri (1.13.6-x86_64-darwin)
+      racc (~> 1.4)
+    nokogiri (1.13.6-x86_64-linux)
+      racc (~> 1.4)
+    nokogumbo (2.0.5)
       nokogiri (~> 1.8, >= 1.8.4)
     parallel (1.20.1)
     pdf-core (0.7.0)
@@ -79,10 +80,11 @@ GEM
     public_suffix (4.0.6)
     pygments.rb (1.2.1)
       multi_json (>= 1.0.0)
+    racc (1.6.0)
     rainbow (3.0.0)
     rake (13.0.1)
     ruby-rc4 (0.1.5)
-    rubyzip (2.3.0)
+    rubyzip (2.3.2)
     safe_yaml (1.0.5)
     thread_safe (0.3.6)
     treetop (1.6.11)
@@ -94,6 +96,7 @@ GEM
 
 PLATFORMS
   x86_64-darwin-19
+  x86_64-linux
 
 DEPENDENCIES
   asciidoctor (= 2.0.12)