[Spec::Lint] Allow a spec out of multiple to fail, and do so gracefully

Closes #3869.

CHANGELOG.md

@@ -13,6 +13,11 @@ To install release candidates run `[sudo] gem install cocoapods --pre`
   [#3842](https://github.com/CocoaPods/CocoaPods/issues/3842)
   [Samuel Giddins](https://github.com/segiddins)
 
+* Show the correct error when `pod spec lint` finds multiple podspecs, and at
+  least one of them fails linting.  
+  [#3869](https://github.com/CocoaPods/CocoaPods/issues/3869)
+  [Samuel Giddins](https://github.com/segiddins)
+
 
 ## 0.38.0
 

lib/cocoapods/command/spec/lint.rb

@@ -72,7 +72,7 @@ module Pod
             raise Informative, if count == 1
                                  "The spec did not pass validation, due to #{failure_reasons.first}."
                                else
-                                 "#{invalid_count} out of #{count} specs failed validation."
+                                 "#{failure_reasons.count} out of #{count} specs failed validation."
                                end
           end
           podspecs_tmp_dir.rmtree if podspecs_tmp_dir.exist?