Validate the CocoaPods version against the specification

lib/cocoapods/installer/analyzer.rb

@@ -451,6 +451,7 @@ module Pod
         UI.section "Resolving dependencies of #{UI.path podfile.defined_in_file}" do
           resolver = Resolver.new(sandbox, podfile, locked_dependencies, sources)
           specs_by_target = resolver.resolve
+          specs_by_target.values.flatten(1).each(&:validate_cocoapods_version)
         end
         specs_by_target
       end

lib/cocoapods/sandbox/podspec_finder.rb

@@ -14,6 +14,7 @@ module Pod
         spec_files.sort_by { |p| -p.to_path.split(File::SEPARATOR).size }.each do |file|
           begin
             spec = Specification.from_file(file)
+            spec.validate_cocoapods_version
             @specs_by_name[spec.name] = spec
           rescue => e
             UI.warn "Unable to load a podspec from `#{file.basename}`, skipping:\n\n#{e}"