Explicitly load style-loader/css-loader deps

This appears to fix sveltejs/sapper-template#27

webpack/config.js

@@ -6,7 +6,12 @@ module.exports = {
 	client: {
 		entry: () => {
 			return {
-				main: entry.client
+				main: [
+					entry.client,
+					// workaround for https://github.com/webpack-contrib/extract-text-webpack-plugin/issues/456
+					'style-loader/lib/addStyles',
+					'css-loader/lib/css-base'
+				]
 			};
 		},
 
@@ -36,4 +41,4 @@ module.exports = {
 			};
 		}
 	}
-};
+};