updates for deploying to Windows

updates for deploying to Windows
1. invalid byte sequence in UTF-8.  [issues like](https://github.com/middleman/middleman/issues/719)
 fixed: update Middleman to 3.0.11  
2. Images are not load on windows. [issues like](https://github.com/middleman/middleman/issues/741)
 fixed: add `gem 'wdm', '~> 0.0.3'` to Gemfile