Enable Lint/AmbiguousOperator rubocop cop

See #17478

.rubocop.yml

@@ -771,7 +771,7 @@ Metrics/PerceivedComplexity:
 # Checks for ambiguous operators in the first argument of a method invocation
 # without parentheses.
 Lint/AmbiguousOperator:
-  Enabled: false
+  Enabled: true
 # Checks for ambiguous regexp literals in the first argument of a method
 # invocation without parentheses.

app/models/project_services/irker_service.rb

@@ -83,7 +83,7 @@ class IrkerService < Service
     self.channels = recipients.split(/\s+/).map do |recipient|
       format_channel(recipient)
     end
-    channels.reject! &:nil?
+    channels.reject!(&:nil?)
   end
   def format_channel(recipient)

lib/api/repositories.rb

@@ -57,7 +57,7 @@ module API
         not_found! "File" unless blob
         content_type 'text/plain'
-        header *Gitlab::Workhorse.send_git_blob(repo, blob)
+        header(*Gitlab::Workhorse.send_git_blob(repo, blob))
       end
       # Get a raw blob contents by blob sha
@@ -83,7 +83,7 @@ module API
         env['api.format'] = :txt
         content_type blob.mime_type
-        header *Gitlab::Workhorse.send_git_blob(repo, blob)
+        header(*Gitlab::Workhorse.send_git_blob(repo, blob))
       end
       # Get a an archive of the repository
@@ -98,7 +98,7 @@ module API
         authorize! :download_code, user_project
         begin
-          header *Gitlab::Workhorse.send_git_archive(user_project, params[:sha], params[:format])
+          header(*Gitlab::Workhorse.send_git_archive(user_project, params[:sha], params[:format]))
         rescue
           not_found!('File')
         end

lib/gitlab/key_fingerprint.rb

@@ -17,9 +17,9 @@ module Gitlab
         file.rewind
         cmd = []
-        cmd.push *%W(ssh-keygen)
-        cmd.push *%W(-E md5) if explicit_fingerprint_algorithm?
-        cmd.push *%W(-lf #{file.path})
+        cmd.push('ssh-keygen')
+        cmd.push('-E', 'md5') if explicit_fingerprint_algorithm?
+        cmd.push('-lf', file.path)
         cmd_output, cmd_status = popen(cmd, '/tmp')
       end