Fix: make .strip_heredoc private

lib/appraisal/cli.rb

@@ -38,6 +38,13 @@ def help(shell, subcommand = false)
       def exit_on_failure?
         true
       end
+
+      private
+
+      def strip_heredoc(string)
+        indent = string.scan(/^[ \t]*(?=\S)/).min.size || 0
+        string.gsub(/^[ \t]{#{indent}}/, "")
+      end
     end
 
     desc "install", "Resolve and install dependencies for each appraisal"
@@ -111,10 +118,5 @@ def method_missing(name, *args, &block)
         end
       end
     end
-
-    def self.strip_heredoc(string)
-      indent = string.scan(/^[ \t]*(?=\S)/).min.size || 0
-      string.gsub(/^[ \t]{#{indent}}/, "")
-    end
   end
 end