Guake 3.6.3 on Ubuntu 19.04 Wayland: Horizontal alignment is ignored

**Describe the bug**

Horizontal alignment is ignored:


**Expected behavior**

When I set horizontal alignment to center or right, and set the width to less than 100%, the Guake window should be aligned accordingly.

**Actual behavior**

When I set horizontal alignment to center or right, and set the width to less than 100%, the Guake window remains left aligned.

**To Reproduce**

* Login into a Gnome Wayland session
* Install Guake 3.6.3 on Ubuntu from https://www.linuxuprising.com/2019/05/new-guake-drop-down-terminal-ppa-ubuntu.html
* Set width to 50% and alignment to center
* Guake remains left-aligned

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$ guake --support

Guake Version: 3.6.3

Vte Version: 0.56.2

Vte Runtime Version: 0.56.2

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GTK+ Version: 3.24.8

GDK Backend: __gi__.GdkWaylandDisplay

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Desktop Session: ubuntu-wayland

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Display: wayland-0

RGBA visual: True

Composited: True

* Monitor: 0 - DEL Dell U4919DW
* Geometry: 5120 x 1440 at 0, 0
* Size: 1200 x 340 mm²
* Primary: False
* Refresh rate: 59.98 Hz
* Subpixel layout: unknown