Add rxjs dependency

package.json

@@ -14,14 +14,17 @@
     "compile": "tsc"
   },
   "devDependencies": {
+    "rxjs-tslint": "^0.1.7",
     "typescript": "^3.4.1"
   },
   "dependencies": {
     "@types/d3": "^5.7.1",
+    "@types/rx": "^4.1.1",
     "d3-axis": "^1.0.12",
     "d3-path": "^1.0.7",
     "d3-scale": "^3.0.0",
     "d3-selection": "^1.4.0",
-    "parcel-bundler": "^1.12.3"
+    "parcel-bundler": "^1.12.3",
+    "rxjs": "^6.4.0"
   }
 }