Change class name of BuildNeed-build association

It should be Ci::Processable because we already use it with
Ci::Build and Ci::Bridge.

app/models/ci/build_need.rb

@@ -6,7 +6,7 @@ module Ci
 
     include BulkInsertSafe
 
-    belongs_to :build, class_name: "Ci::Build", foreign_key: :build_id, inverse_of: :needs
+    belongs_to :build, class_name: "Ci::Processable", foreign_key: :build_id, inverse_of: :needs
 
     validates :build, presence: true
     validates :name, presence: true, length: { maximum: 128 }

spec/models/ci/build_need_spec.rb

@@ -5,7 +5,7 @@ require 'spec_helper'
 RSpec.describe Ci::BuildNeed, model: true do
   let(:build_need) { build(:ci_build_need) }
 
-  it { is_expected.to belong_to(:build) }
+  it { is_expected.to belong_to(:build).class_name('Ci::Processable') }
 
   it { is_expected.to validate_presence_of(:build) }
   it { is_expected.to validate_presence_of(:name) }