Add Angular v8 downstream test

Author: oliverguenther

downstream_projects.json

@@ -2,6 +2,7 @@
   "angular5": "./test-angular-versions/v5",
   "angular6": "./test-angular-versions/v6",
   "angular7": "./test-angular-versions/v7",
+  "angular8": "./test-angular-versions/v8",
   "typescript2.3": "./test-typescript-versions/typescript2.3",
   "typescript2.4": "./test-typescript-versions/typescript2.4",
   "typescript2.5": "./test-typescript-versions/typescript2.5",