Pin Jekyll and a few other Ruby gems

Gemfile

@@ -11,7 +11,7 @@ gem "rubygems-update", "~> 3.4"
 #
 # This will help ensure the proper Jekyll version is running.
 # Happy Jekylling!
-gem "jekyll", ">= 4"
+gem "jekyll", "~> 4.0"
 
 # This is the default theme for new Jekyll sites. You may change this to anything you like.
 #gem "minima", "~> 2.0"
@@ -23,13 +23,15 @@ gem "jekyll", ">= 4"
 # If you have any plugins, put them here!
 group :jekyll_plugins do
    gem "jekyll-feed", "~> 0.6"
+   gem "jekyll-compose"
+   gem "jekyll-scholar", "~> 7.1"
+   gem "jekyll-twitter-plugin"
 end
 
 # Windows does not include zoneinfo files, so bundle the tzinfo-data gem
-gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]
-gem 'jekyll-compose', group: [:jekyll_plugins]
-gem 'jekyll-scholar'
-gem 'html-proofer'
-gem 'jekyll-twitter-plugin'
+gem "tzinfo-data", platforms: [:mingw, :mswin, :x64_mingw, :jruby]
+
+# Other gems.
+gem "html-proofer"
 gem "nokogiri", ">= 1.10.8"
-gem "bibtex-ruby", ">= 5.1.0"
+gem "bibtex-ruby", ">= 5.1.1"

Gemfile.lock

@@ -131,12 +131,12 @@ PLATFORMS
   x86_64-linux
 
 DEPENDENCIES
-  bibtex-ruby (>= 5.1.0)
+  bibtex-ruby (>= 5.1.1)
   html-proofer
-  jekyll (>= 4)
+  jekyll (~> 4.0)
   jekyll-compose
   jekyll-feed (~> 0.6)
-  jekyll-scholar
+  jekyll-scholar (~> 7.1)
   jekyll-twitter-plugin
   nokogiri (>= 1.10.8)
   rubygems-update (~> 3.4)