The Inappbrowser plugin prompts a download above ios version 13

# Bug Report
The plugin usually should open the pdf in the in-app browser. But in ios version 13 and above, the user is forced to download the pdf in order to view it.
## Problem

### What is expected to happen?

The pdf is expected to open without forcing the user to download

### What does actually happen?

The user is able to see the pdf only after downloading

## Information

Using iab.create to open the pdf.

### Command or Code

### Environment, Platform, Device

Platform : ios
Version: 13 and above only

### Version information

cli packages:
@ionic/cli-utils : 1.18.0
ionic (Ionic CLI) : 3.18.0
System:
Node : v6.11.0
npm : 3.10.10
OS : macOS
Misc:
backend : pro

Xcode: 10.2.1

## Checklist

- [x] I searched for existing GitHub issues
- [ ] I updated all Cordova tooling to most recent version
- [x] I included all the necessary information above

Reproduce the iab.create PDF flow on iOS 13 and newer, then inspect the plugin's iOS implementation for how PDF URLs are opened. Done means the PDF opens in the in-app browser without requiring a download; the report does not name a source file or regression test.

Written by the indexing model from the issue text.