chore: update Gemfile. Close #37

Gemfile.lock

@@ -4,15 +4,15 @@ GEM
     addressable (2.8.6)
       public_suffix (>= 2.0.2, < 6.0)
     colorator (1.1.0)
-    concurrent-ruby (1.2.2)
+    concurrent-ruby (1.3.3)
     em-websocket (0.5.3)
       eventmachine (>= 0.12.9)
       http_parser.rb (~> 0)
     eventmachine (1.2.7)
-    ffi (1.16.3)
+    ffi (1.17.0-x86_64-darwin)
     forwardable-extended (2.6.0)
     http_parser.rb (0.8.0)
-    i18n (1.14.1)
+    i18n (1.14.5)
       concurrent-ruby (~> 1.0)
     jekyll (4.1.1)
       addressable (~> 2.4)
@@ -38,21 +38,23 @@ GEM
     kramdown-parser-gfm (1.1.0)
       kramdown (~> 2.0)
     liquid (4.0.4)
-    listen (3.8.0)
+    listen (3.9.0)
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
     mercenary (0.4.0)
     pathutil (0.16.2)
       forwardable-extended (~> 2.6)
-    public_suffix (5.0.4)
+    public_suffix (5.1.1)
     rb-fsevent (0.11.2)
-    rb-inotify (0.10.1)
+    rb-inotify (0.11.1)
       ffi (~> 1.0)
-    rexml (3.2.6)
+    rexml (3.3.0)
+      strscan
     rouge (3.30.0)
     safe_yaml (1.0.5)
     sassc (2.4.0)
       ffi (~> 1.9)
+    strscan (3.1.0)
     terminal-table (1.8.0)
       unicode-display_width (~> 1.1, >= 1.1.1)
     unicode-display_width (1.8.0)