build(aio): downgrade sass-loader due to a regression

See webpack-contrib/sass-loader#450

Author: IgorMinar

aio/package.json

@@ -48,6 +48,7 @@
     "@angular/service-worker": "^1.0.0-beta.11",
     "core-js": "^2.4.1",
     "rxjs": "^5.3.1",
+    "sass-loader": "6.0.3",
     "zone.js": "^0.8.10"
   },
   "devDependencies": {

aio/yarn.lock

@@ -6081,6 +6081,16 @@ sass-graph@^2.1.1:
     lodash "^4.0.0"
     yargs "^4.7.1"
 
+sass-loader@6.0.3:
+  version "6.0.3"
+  resolved "https://registry.yarnpkg.com/sass-loader/-/sass-loader-6.0.3.tgz#33983b1f90d27ddab0e57d0dac403dce9bc7ecfd"
+  dependencies:
+    async "^2.1.5"
+    clone-deep "^0.2.4"
+    loader-utils "^1.0.1"
+    lodash.tail "^4.1.1"
+    pify "^2.3.0"
+
 sass-loader@^6.0.3:
   version "6.0.4"
   resolved "https://registry.yarnpkg.com/sass-loader/-/sass-loader-6.0.4.tgz#e1f20f534e8514445b9362deb566a4c40440d98d"