Fix CSS and JS hashes for 4.0.0-alpha.4 (twbs#20692) (twbs#20694)

Author: akamch

_config.yml

@@ -38,9 +38,9 @@ themes:           http://themes.getbootstrap.com
 cdn:
   # See https://www.srihash.org for info on how to generate the hashes
   css:            https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.4/css/bootstrap.min.css
-  css_hash:       "2hfp1SzUoho7/TsGGGDaFdsuuDL0LX2hnUp6VkX3CUQ2K4K+xjboZdsXyp4oUHZj"
+  css_hash:       "sha384-2hfp1SzUoho7/TsGGGDaFdsuuDL0LX2hnUp6VkX3CUQ2K4K+xjboZdsXyp4oUHZj"
   js:             https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.4/js/bootstrap.min.js
-  js_hash:        "VjEeINv9OSwtWFLAtmc4JCtEJXXBub00gtSnszmspDLCtC0I4z4nqz7rEFbIZLLU"
+  js_hash:        "sha384-VjEeINv9OSwtWFLAtmc4JCtEJXXBub00gtSnszmspDLCtC0I4z4nqz7rEFbIZLLU"
   jquery:         https://ajax.googleapis.com/ajax/libs/jquery/3.0.0/jquery.min.js
   jquery_hash:    "sha384-THPy051/pYDQGanwU6poAc/hOdQxjnOEXzbT+OuUAFqNqFjL+4IGLBgCJC3ZOShY"
   tether:         https://cdnjs.cloudflare.com/ajax/libs/tether/1.2.0/js/tether.min.js