Merge pull request #904 from meganemura/use-dir-exist

Replace deprecated Dir.exists? with Dir.exist?

lib/guard/templates/Guardfile

@@ -3,7 +3,7 @@
 ## Uncomment and set this to only include directories you want to watch
 # directories %w(app lib config test spec features) \
-#  .select{|d| Dir.exists?(d) ? d : UI.warning("Directory #{d} does not exist")}
+#  .select{|d| Dir.exist?(d) ? d : UI.warning("Directory #{d} does not exist")}
 ## Note: if you are using the `directories` clause above and you are not
 ## watching the project directory ('.'), then you will want to move