Update spec build to Jekyll 3.3

Seth Tisue suggested updating the Jekyll dependency for the Scala spec
in scala/scala-lang#559 so that is consistent with the scala-lang.org
and docs.scala-lang.org Web sites.

Upgrading Jekll from 2.5.3 to 3.3.0 produces slight differences in the
HTML output.  The differences in the HTML are isolated to the markup
for source code highlighting.  In the spec, those are Scala code
listings and the blocks of extended-BNF. From what I saw looking at
all the pages, they render exactly the same, pixel-for-pixel, as
before.  I hit print preview and also didn't notice any anomalies.

I tested in Ruby 2.2.5 using rbenv 0.4.0, gem 2.4.5.1 and Bundler
1.13.6.  This is compared to the Travis build that uses Ruby 2.2.0p0
using rvm 1.26.10, gem 2.4.5 and Bundler 1.7.9.

1 files changed, 1 insertions, 1 deletions

diff --git a/Gemfile b/Gemfile
index c8c926dfde..f91279b3e6 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,7 +1,7 @@
 # To build the spec on Travis CI
 source "https://rubygems.org"
 
-gem "jekyll", "2.5.3"
+gem "jekyll", "3.3.0"
 gem "rouge"
 # gem 's3_website'
 gem "redcarpet", "3.3.2"