chore(deps): update jekyll (3.9.3 → 3.9.4) (#894)

| datasource | package | from  | to    |
| ---------- | ------- | ----- | ----- |
| rubygems   | jekyll  | 3.9.3 | 3.9.4 |

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

docs/Gemfile.lock

@@ -6,7 +6,7 @@ GEM
       i18n (>= 1.6, < 2)
       minitest (>= 5.1)
       tzinfo (~> 2.0)
-    addressable (2.8.4)
+    addressable (2.8.6)
       public_suffix (>= 2.0.2, < 6.0)
     coffee-script (2.4.1)
       coffee-script-source
@@ -30,7 +30,6 @@ GEM
       ruby2_keywords (>= 0.0.4)
     faraday-net_http (3.0.2)
     ffi (1.15.5)
-    ffi (1.15.5-x64-mingw32)
     forwardable-extended (2.6.0)
     gemoji (3.0.1)
     github-pages (228)
@@ -231,7 +230,7 @@ GEM
     rb-fsevent (0.11.2)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    rexml (3.2.5)
+    rexml (3.2.6)
     rouge (3.26.0)
     ruby2_keywords (0.0.5)
     rubyzip (2.3.2)