Fix grammar in Danger roulette timezone details

lib/gitlab/danger/teammate.rb

@@ -82,7 +82,7 @@ module Gitlab
         diff = floored_offset_hours - author.floored_offset_hours
         return "same timezone as `@#{author.username}`" if diff.zero?
 
-        ahead_or_behind = diff < 0 ? 'behind' : 'ahead'
+        ahead_or_behind = diff < 0 ? 'behind' : 'ahead of'
         pluralized_hours = pluralize(diff.abs, 'hour', 'hours')
 
         "#{pluralized_hours} #{ahead_or_behind} `@#{author.username}`"

spec/lib/gitlab/danger/teammate_spec.rb

@@ -192,12 +192,12 @@ RSpec.describe Gitlab::Danger::Teammate do
       context 'when author is given' do
         where(:tz_offset_hours, :author_offset, :diff_text) do
           -12 | -10 | "2 hours behind `@mario`"
-          -10 | -12 | "2 hours ahead `@mario`"
+          -10 | -12 | "2 hours ahead of `@mario`"
           -10 | 2 | "12 hours behind `@mario`"
           2 | 4 | "2 hours behind `@mario`"
-          4 | 2 | "2 hours ahead `@mario`"
+          4 | 2 | "2 hours ahead of `@mario`"
           2 | 3 | "1 hour behind `@mario`"
-          3 | 2 | "1 hour ahead `@mario`"
+          3 | 2 | "1 hour ahead of `@mario`"
           2 | 2 | "same timezone as `@mario`"
         end