[Sass] Suggest using --in-place when converting sass2 to sass3.

doc-src/SASS_CHANGELOG.md

@@ -3,6 +3,11 @@
 * Table of contents
 {:toc}
 
+## 3.0.9 (Unreleased)
+
+* When using `sass-convert --from sass2 --to sass --recursive`,
+  suggest the use of `--in-place` as well.
+
 ## 3.0.8
 
 [Tagged on GitHub](http://github.com/nex3/haml/commit/3.0.8).

lib/haml/exec.rb

@@ -710,6 +710,8 @@ END
         end
         @options[:output] ||= @options[:input]
 
+        from = @options[:from]
+        from = :sass if from == :sass2
         if @options[:to] == @options[:from] && !@options[:in_place]
           fmt = @options[:from]
           raise "Error: converting from #{fmt} to #{fmt} without --in-place"