Fix build with Ruby 2.6

Gemfile

@@ -1,12 +1,16 @@
 source "https://rubygems.org"
 
 gem "jekyll"
-gem "webrick"
+gem "webrick", "~> 1.7"
 gem "json"
+gem "sassc", "2.1"
+gem "bigdecimal"
+gem "logger"
 
 group :jekyll_plugins do
   gem "jekyll-feed"
   gem "jekyll-paginate"
   gem "jekyll-sitemap"
   gem "jekyll-redirect-from"
+  gem "jekyll-sass-converter", "~> 2.0"
 end

Gemfile.lock

@@ -1,35 +1,52 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    addressable (2.8.0)
-      public_suffix (>= 2.0.2, < 5.0)
+    addressable (2.8.7)
+      public_suffix (>= 2.0.2, < 7.0)
+    base64 (0.2.0)
+    bigdecimal (3.1.9)
     colorator (1.1.0)
-    concurrent-ruby (1.1.10)
+    concurrent-ruby (1.3.5)
+    csv (3.3.2)
     em-websocket (0.5.3)
       eventmachine (>= 0.12.9)
       http_parser.rb (~> 0)
     eventmachine (1.2.7)
-    ffi (1.15.5)
+    ffi (1.17.1)
+    ffi (1.17.1-aarch64-linux-gnu)
+    ffi (1.17.1-aarch64-linux-musl)
+    ffi (1.17.1-arm-linux-gnu)
+    ffi (1.17.1-arm-linux-musl)
+    ffi (1.17.1-arm64-darwin)
+    ffi (1.17.1-x86-linux-gnu)
+    ffi (1.17.1-x86-linux-musl)
+    ffi (1.17.1-x86_64-darwin)
+    ffi (1.17.1-x86_64-linux-gnu)
+    ffi (1.17.1-x86_64-linux-musl)
     forwardable-extended (2.6.0)
     http_parser.rb (0.8.0)
-    i18n (1.10.0)
+    i18n (1.14.7)
       concurrent-ruby (~> 1.0)
-    jekyll (4.2.2)
+    jekyll (4.4.1)
       addressable (~> 2.4)
+      base64 (~> 0.2)
       colorator (~> 1.0)
+      csv (~> 3.0)
       em-websocket (~> 0.5)
       i18n (~> 1.0)
-      jekyll-sass-converter (~> 2.0)
+      jekyll-sass-converter (>= 2.0, < 4.0)
       jekyll-watch (~> 2.0)
-      kramdown (~> 2.3)
+      json (~> 2.6)
+      kramdown (~> 2.3, >= 2.3.1)
       kramdown-parser-gfm (~> 1.0)
       liquid (~> 4.0)
-      mercenary (~> 0.4.0)
+      mercenary (~> 0.3, >= 0.3.6)
       pathutil (~> 0.9)
-      rouge (~> 3.0)
+      rouge (>= 3.0, < 5.0)
       safe_yaml (~> 1.0)
-      terminal-table (~> 2.0)
-    jekyll-feed (0.16.0)
+      terminal-table (>= 1.8, < 4.0)
+      webrick (~> 1.7)
+    jekyll-feed (0.17.0)
       jekyll (>= 3.7, < 5.0)
     jekyll-paginate (1.1.0)
     jekyll-redirect-from (0.16.0)
@@ -40,43 +57,62 @@ GEM
       jekyll (>= 3.7, < 5.0)
     jekyll-watch (2.2.1)
       listen (~> 3.0)
-    json (2.7.1)
-    kramdown (2.4.0)
-      rexml
+    json (2.10.1)
+    kramdown (2.5.1)
+      rexml (>= 3.3.9)
     kramdown-parser-gfm (1.1.0)
       kramdown (~> 2.0)
-    liquid (4.0.3)
-    listen (3.7.1)
+    liquid (4.0.4)
+    listen (3.9.0)
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
+    logger (1.7.0)
     mercenary (0.4.0)
     pathutil (0.16.2)
       forwardable-extended (~> 2.6)
-    public_suffix (4.0.7)
-    rb-fsevent (0.11.1)
-    rb-inotify (0.10.1)
+    public_suffix (6.0.1)
+    rb-fsevent (0.11.2)
+    rb-inotify (0.11.1)
       ffi (~> 1.0)
-    rexml (3.2.5)
-    rouge (3.28.0)
+    rexml (3.4.1)
+    rouge (4.5.1)
     safe_yaml (1.0.5)
-    sassc (2.4.0)
+    sassc (2.1.0)
       ffi (~> 1.9)
-    terminal-table (2.0.0)
-      unicode-display_width (~> 1.1, >= 1.1.1)
-    unicode-display_width (1.8.0)
-    webrick (1.7.0)
+    sassc (2.1.0-x86-linux)
+      ffi (~> 1.9)
+    sassc (2.1.0-x86_64-linux)
+      ffi (~> 1.9)
+    terminal-table (3.0.2)
+      unicode-display_width (>= 1.1.1, < 3)
+    unicode-display_width (2.6.0)
+    webrick (1.9.1)
 
 PLATFORMS
-  x86_64-linux
+  aarch64-linux-gnu
+  aarch64-linux-musl
+  arm-linux-gnu
+  arm-linux-musl
+  arm64-darwin
+  ruby
+  x86-linux-gnu
+  x86-linux-musl
+  x86_64-darwin
+  x86_64-linux-gnu
+  x86_64-linux-musl
 
 DEPENDENCIES
+  bigdecimal
   jekyll
   jekyll-feed
   jekyll-paginate
   jekyll-redirect-from
+  jekyll-sass-converter (~> 2.0)
   jekyll-sitemap
   json
-  webrick
+  logger
+  sassc (= 2.1)
+  webrick (~> 1.7)
 
 BUNDLED WITH
-   2.3.10
+   2.6.0