MarkerOptions.anchor doesn't affect on position

package.json:
```
...
"@ionic-native/core": "^5.0.0",
"@ionic-native/device": "^5.21.6",
"@ionic-native/google-maps": "^5.27.0-beta-20200630",
"@ionic/angular": "^5.0.4",
"cordova-browser": "6.0.0"
...
```
using cordova browser.
```
this.map.addMarker({
position: {lat: this.lat, lng: this.lon},
icon: {
url: '../../assets/icon/eye.png',

size: {
width: 32,
height: 32
}
},
anchor: [16, 16]
})
```
the marker appears at the same place in any anchor

Reproduce the marker behavior in a Cordova browser using the package.json versions and the map.addMarker example. Trace how the anchor option is handled for the marker and verify that changing anchor changes the rendered marker position.

索引モデルが issue の本文から書いたものです。