Merge branch 'complexity/rubocop-style-loop' into 'master'

Enable Style/InfiniteLoop Rubocop cop

This MR enabled Style/InfiniteLoop Rubocop cop, and fixes offenses.

See https://gitlab.com/gitlab-org/gitlab-ce/issues/17478

See merge request !4257

.rubocop.yml

@@ -299,7 +299,7 @@ Style/IndentHash:
 
 # Use Kernel#loop for infinite loops.
 Style/InfiniteLoop:
-  Enabled: false
+  Enabled: true
 
 # Use the new lambda literal syntax for single-line blocks.
 Style/Lambda:

app/models/network/graph.rb

@@ -253,7 +253,7 @@ module Network
       leaves = []
       leaves.push(commit) if commit.space.zero?
 
-      while true
+      loop do
         return leaves if commit.parents(@map).count.zero?
 
         commit = commit.parents(@map).first