ref: Also fix traceHeaders

Author: HazAT

packages/apm/src/hubextensions.ts

@@ -6,10 +6,8 @@ import { Span } from './span';
 import { Transaction } from './transaction';
 
 /** Returns all trace headers that are currently on the top scope. */
-function traceHeaders(): { [key: string]: string } {
-  // @ts-ignore
-  const that = this as Hub;
-  const scope = that.getScope();
+function traceHeaders(this: Hub): { [key: string]: string } {
+  const scope = this.getScope();
   if (scope) {
     const span = scope.getSpan();
     if (span) {