refactor(directline): update rxjs to v6, use rxjs pipeable operators, update webpack to v4

Author: harshithkashyap

.gitignore

@@ -5,3 +5,5 @@ built
 /directLine.js.map
 
 npm-debug.log
+
+dist/

package-lock.json

@@ -20,12 +20,14 @@
   "author": "Microsoft Corp",
   "license": "MIT",
   "dependencies": {
-    "rxjs": "^5.0.3"
+    "rxjs": "6.1.0"
   },
   "devDependencies": {
     "source-map-loader": "^0.1.5",
     "ts-loader": "^1.3.3",
-    "typescript": "^2.3.2",
-    "webpack": "^1.14.0"
+    "typescript": "2.7.2",
+    "uglifyjs-webpack-plugin": "^1.2.5",
+    "webpack": "4.8.3",
+    "webpack-cli": "^2.1.3"
   }
 }