chore(package): Remove RxJS peer dep.

Author: cartant

package.json

@@ -53,7 +53,6 @@
   "name": "rxjs-tslint-rules",
   "optionalDependencies": {},
   "peerDependencies": {
-    "rxjs": "^5.0.0 || ^6.0.0 || ^7.0.0-beta.0",
     "tslint": "^5.0.0 || ^6.0.0",
     "typescript": "^2.3.0 || ^3.0.0 || ^4.0.0"
   },