[Lockfile] Cache the spec repos by pod so the hash only needs to be t…

…raversed once

lib/cocoapods-core/lockfile.rb

@@ -101,7 +101,7 @@ def version(pod_name)
     # @return [Nil] If there is no source stored for the given name.
     #
     def spec_repo(pod_name)
-      pods_by_spec_repo.detect { |key, values| break key if values.include?(pod_name) }
+      spec_repos_by_pod[pod_name]
     end
 
     # Returns the checksum for the given Pod.
@@ -248,6 +248,17 @@ def checksum_data
       internal_data['SPEC CHECKSUMS'] || {}
     end
 
+    # @return [Hash{String => String}] A hash containing the spec repo used for the specification
+    #         by the name of the root spec.
+    #
+    def spec_repos_by_pod
+      @spec_repos_by_pod ||= pods_by_spec_repo.each_with_object({}) do |(spec_repo, pods), spec_repos_by_pod|
+        pods.each do |pod|
+          spec_repos_by_pod[pod] = spec_repo
+        end
+      end
+    end
+
     #-------------------------------------------------------------------------#
 
     # !@group Comparison with a Podfile