Update gem dependencies

- Add Jekyll plugins needed for the theme to .gemspec
- Remove Jekyll plugin gems from example site as they are installed with the theme

example/Gemfile

@@ -14,7 +14,7 @@ source "https://rubygems.org"
 # If you want to use Jekyll native, uncomment the line below.
 # To upgrade, run `bundle update`.
 
-gem "jekyll", :git => "https://github.com/jekyll/jekyll.git"
+gem "jekyll", "~> 3.3"
 gem "minimal-mistakes-jekyll", path: "../"
 
 gem "wdm", "~> 0.1.0" if Gem.win_platform?
@@ -22,9 +22,9 @@ gem "wdm", "~> 0.1.0" if Gem.win_platform?
 # If you have any plugins, put them here!
 group :jekyll_plugins do
   # gem "jekyll-archives"
-  gem "jekyll-paginate"
-  gem "jekyll-sitemap"
-  gem "jekyll-gist"
-  gem "jekyll-feed"
-  gem "jemoji"
+  # gem "jekyll-paginate"
+  # gem "jekyll-sitemap"
+  # gem "jekyll-gist"
+  # gem "jekyll-feed"
+  # gem "jemoji"
 end