message: Update ajax.ts
  Incorrect *this* is referred in the overridden anonymous function handler of XMLHttpRequest prototype.
  Fixes for the issue
diff: @@ -106,7 +106,7 @@ export class AjaxMonitor implements ITelemetryPlugin, IDependenciesPlugin, IInst
  ajaxMonitorInstance.openHandler(this, method, url, async);
  }
  } catch (e) {
  - this._core.logger.throwInternal(
  + ajaxMonitorInstance._core.logger.throwInternal(
  LoggingSeverity.CRITICAL,
  _InternalMessageId.FailedMonitorAjaxOpen,
  "Failed to monitor XMLHttpRequest.open, monitoring data for this ajax call may be incorrect.",
  @@ -161,7 +161,7 @@ export class AjaxMonitor implements ITelemetryPlugin, IDependenciesPlugin, IInst
  ajaxMonitorInstance.sendHandler(this, content);
  }
  } catch (e) {
  - this._core.logger.throwInternal(
  + ajaxMonitorInstance._core.logger.throwInternal(
  LoggingSeverity.CRITICAL,
  _InternalMessageId.FailedMonitorAjaxSend,
  "Failed to monitor XMLHttpRequest, monitoring data for this ajax call may be incorrect.",
  @@ -191,7 +191,7 @@ export class AjaxMonitor implements ITelemetryPlugin, IDependenciesPlugin, IInst
  (<XMLHttpRequestInstrumented>this).ajaxData.xhrMonitoringState.abortDone = true;
  }
  } catch (e) {
  - this._core.logger.throwInternal(
  + ajaxMonitorInstance._core.logger.throwInternal(
  LoggingSeverity.CRITICAL,
  _InternalMessageId.FailedMonitorAjaxAbort,
  "Failed to monitor XMLHttpRequest.abort, monitoring data for this ajax call may be incorrect.",
  @@ -219,7 +219,7 @@ export class AjaxMonitor implements ITelemetryPlugin, IDependenciesPlugin, IInst
  // ignore messages with c00c023f, as this a known IE9 XHR abort issue
  if (!exceptionText || exceptionText.toLowerCase().indexOf("c00c023f") == -1) {
  - this._core.logger.throwInternal(
  + ajaxMonitorInstance._core.logger.throwInternal(
  LoggingSeverity.CRITICAL,
  _InternalMessageId.FailedMonitorAjaxRSC,
  "Failed to monitor XMLHttpRequest 'readystatechange' event handler, monitoring data for this ajax call may be incorrect.",
  