[SpecWithSource] Rename #spec_source for consistency with LazySpecification

Gemfile.lock

@@ -7,7 +7,7 @@ GIT
 
 GIT
   remote: https://github.com/CocoaPods/Core.git
-  revision: b24b82511b8ed5a6f93e2a9f74bbdc9c33da8672
+  revision: 1f8ced657a224eabeba6958d130ee04058d91f60
   branch: master
   specs:
     cocoapods-core (1.4.0)
@@ -180,7 +180,7 @@ GEM
     gh_inspector (1.1.1)
     git (1.3.0)
     hashdiff (0.3.1)
-    i18n (0.9.3)
+    i18n (0.9.5)
       concurrent-ruby (~> 1.0)
     inch (0.7.0)
       pry

lib/cocoapods/resolver.rb

@@ -137,8 +137,9 @@ module Pod
             group_by(&:first).
             map do |vertex, spec_test_only_tuples|
               test_only = spec_test_only_tuples.all? { |tuple| tuple[1] }
-              spec_source = vertex.payload.respond_to?(:spec_source) && vertex.payload.spec_source
-              ResolverSpecification.new(vertex.payload, test_only, spec_source)
+              payload = vertex.payload
+              spec_source = payload.respond_to?(:spec_source) && payload.spec_source
+              ResolverSpecification.new(payload, test_only, spec_source)
             end.
             sort_by(&:name)
         end

lib/cocoapods/resolver/lazy_specification.rb

@@ -3,10 +3,10 @@ module Pod
   class Specification
     class Set
       class SpecWithSource < DelegateClass(Specification)
-        attr_reader :spec_repo
+        attr_reader :spec_source
         def initialize(spec, source)
           super(spec)
-          @spec_repo = source
+          @spec_source = source
         end
 
         undef is_a?