[Linter] Demoted post_install hook message to note.

lib/cocoapods/command/spec.rb

@@ -185,6 +185,7 @@ module Pod
               @platform_notes[platform]    << "#{platform.name} [!] Fatal errors found skipping the rest of the validation"
             else
               @platform_warnings[platform] += podspec_warnings + deprecation_warnings
+              @platform_notes[platform]    += podspec_notes
               peform_extensive_analysis unless quick
             end
           end
@@ -336,6 +337,14 @@ module Pod
           @spec.source && @spec.source[:git] =~ /github.com/
         end
 
+        # @return [Array<String>] List of the comments detected in the podspec
+        def podspec_notes
+          text = @file.read
+          deprecations = []
+          deprecations << "The `post_install' hook is reserved for edge cases"          if text. =~ /post_install/
+          deprecations
+        end
+
         # It reads a podspec file and checks for strings corresponding
         # to features that are or will be deprecated
         #
@@ -346,7 +355,6 @@ module Pod
           deprecations = []
           deprecations << "`config.ios?' and `config.osx?' are deprecated"              if text. =~ /config\..?os.?/
           deprecations << "clean_paths are deprecated and ignored (use preserve_paths)" if text. =~ /clean_paths/
-          deprecations << "The `post_install' hook is reserved for edge cases"          if text. =~ /post_install/
           deprecations
         end