Fix rubocop errors

app/controllers/ci/lints_controller.rb

@@ -11,7 +11,7 @@ module Ci
       if @content.blank?
         @status = false
         @error = "Please provide content of .gitlab-ci.yml"
-      elsif Ci::GitlabCiYamlProcessor.errors(@content) != nil
+      elsif !Ci::GitlabCiYamlProcessor.errors(@content).nil?
         @status = false
         @error = Ci::GitlabCiYamlProcessor.errors(@content)
       else

lib/api/lint.rb

@@ -13,7 +13,7 @@ module API
           jobs: []
         }
-        if Ci::GitlabCiYamlProcessor.errors(@content) != nil
+        if !Ci::GitlabCiYamlProcessor.errors(@content).nil?
           status 200
           response[:errors].push(Ci::GitlabCiYamlProcessor.errors(@content))
           response[:status] = 'invalid'