Upgrade Jekyll to 2.8.5 to fix URL bugs

We upgraded Jekyll to 2.6.3 (a minor version upgrade from 2.4.3) to fix a security vulnerability, but the entire 2.6.x line has a bug with how URLs are handled in the built-in web server. (Fixed here: jekyll/jekyll#6459 and jekyll/jekyll#6475, originally introduced in the fix to jekyll/jekyll#6222 (comment)).

Anyway, 2.8.5 includes a fix and generates an identical `_site` directory on disk, so should be all good.

Gemfile

@@ -9,7 +9,7 @@ ruby '~> 2.3'
 #
 # This will help ensure the proper Jekyll version is running.
 # Happy Jekylling!
-gem "jekyll", "3.6.3"
+gem "jekyll", "3.8.5"
 
 # This is the default theme for new Jekyll sites. You may change this to anything you like.
 gem "minima", "~> 2.0"

Gemfile.lock

@@ -4,26 +4,36 @@ GEM
     addressable (2.6.0)
       public_suffix (>= 2.0.2, < 4.0)
     colorator (1.1.0)
+    concurrent-ruby (1.1.4)
+    em-websocket (0.5.1)
+      eventmachine (>= 0.12.9)
+      http_parser.rb (~> 0.6.0)
+    eventmachine (1.2.7)
     ffi (1.10.0)
     forwardable-extended (2.6.0)
-    jekyll (3.6.3)
+    http_parser.rb (0.6.0)
+    i18n (0.9.5)
+      concurrent-ruby (~> 1.0)
+    jekyll (3.8.5)
       addressable (~> 2.4)
       colorator (~> 1.0)
+      em-websocket (~> 0.5)
+      i18n (~> 0.7)
       jekyll-sass-converter (~> 1.0)
-      jekyll-watch (~> 1.1)
+      jekyll-watch (~> 2.0)
       kramdown (~> 1.14)
       liquid (~> 4.0)
       mercenary (~> 0.3.3)
       pathutil (~> 0.9)
-      rouge (>= 1.7, < 3)
+      rouge (>= 1.7, < 4)
       safe_yaml (~> 1.0)
     jekyll-feed (0.9.2)
       jekyll (~> 3.3)
     jekyll-redirect-from (0.12.1)
       jekyll (~> 3.3)
     jekyll-sass-converter (1.5.2)
       sass (~> 3.4)
-    jekyll-watch (1.5.1)
+    jekyll-watch (2.1.2)
       listen (~> 3.0)
     kramdown (1.17.0)
     liquid (4.0.1)
@@ -47,7 +57,7 @@ GEM
     rb-fsevent (0.10.3)
     rb-inotify (0.10.0)
       ffi (~> 1.0)
-    rouge (2.2.1)
+    rouge (3.3.0)
     ruby_dep (1.5.0)
     safe_yaml (1.0.4)
     sass (3.7.3)
@@ -60,7 +70,7 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
-  jekyll (= 3.6.3)
+  jekyll (= 3.8.5)
   jekyll-feed (~> 0.6)
   jekyll-redirect-from
   minima (~> 2.0)