fix(package): require Angular >= v8 as peer dependency

Author: gund

projects/ngx-testing/package.json

@@ -19,8 +19,8 @@
     "bindings"
   ],
   "peerDependencies": {
-    "@angular/common": "^8.0.0",
-    "@angular/core": "^8.0.0",
-    "@angular/platform-browser": "^8.0.0"
+    "@angular/common": ">=8.0.0",
+    "@angular/core": ">=8.0.0",
+    "@angular/platform-browser": ">=8.0.0"
   }
 }