feat: capacitor localnotification image is not showing

# Bug Report

Latest Dependencies:

@capacitor/cli: 1.4.0

@capacitor/core: 1.4.0

@capacitor/android: 1.4.0

@capacitor/ios: 1.4.0

## Affected Platform(s)
I tested it on Android and web also

- [x] Android
- [ ] iOS
- [ ] Electron
- [x] Web

## Current Behavior
when showing notification no image is shown in the notification

## Expected Behavior
when adding url and id to attachments it should show image in notification

## Sample Code or Sample Application Repo
```
LocalNotifications.schedule({
notifications: [
{
title: "aaaa",
body: "Body",
id: 1,
actionTypeId: 'OPEN_PRODUCT',
attachments: [
{ id: 'face', url: 'https://khanoo.com/wp-content/uploads/estate_images/house/77-1576179614/230174.jpg' }
],
schedule: {
every: "minute"
},

extra: null
}
]
});
```

## Reproduction Steps

Just test my code which i provided to see if you can see image or not

## Other Technical Details

`npm --version` output: 6.13.4

`node --version` output: v12.13.1

`pod --version` output (iOS issues only): 1.9.0.beta.2