Fix some linting suggestions from rubocop

lib/tasks/gitlab/banzai.rake

@@ -3,12 +3,12 @@
 namespace :gitlab do
   namespace :banzai do
     desc 'GitLab | Banzai | Render markdown using our FullPipeline (input will be requested)'
-    task :render => :environment do |_t|
-      markdown = Array.new
+    task render: :environment do |_t|
+      markdown = []
 
       puts "\nEnter markdown below, Ctrl-D to end (if you need blank lines, paste in the full text):"
-      while buf = Readline.readline('', true) do
-	      markdown << buf
+      while buf = Readline.readline('', true)
+        markdown << buf
       end
 
       puts "Rendering using Gitlab's FullPipeline...\n\n"