Vega mark positioning is breaking from 6.4.0 to 6.5.0

[clemlesne]

Hello,

Kibana version: 6.5.0

Elasticsearch version: 6.5.0

Server OS version: Linux

Browser version: Chrome Version 64.0.3282.119

Browser OS version: Windows 10

Original install method (e.g. download page, yum, from source, etc.): n/a

Description of the problem including expected versus actual behavior:
I use Kibana with vega to create custom text based visualizations. For this I use this configuration:

{
  type: text
  encode: {
    update: {
      text: {value: "Fully processed requests"}
      align: {value: "center"}
      baseline: {value: "middle"}
      xc: {signal: "width/2"}
      yc: {signal: "height/2"}
      fontSize: {value: "14"}
    }
  }
}

But, since the upgrade from Kibana & Elastic 6.4.0 to 6.5.0, all these visualizations are rendering in the upper top (screenshot included).

This is the same render in all my dashboards.

Steps to reproduce:

1. Create a Vega visualization
2. Create a mark with my configuration
3. Observe

Errors in browser console (if relevant): none

Provide logs and/or server output (if relevant): none

[elasticmachine]

Pinging @elastic/kibana-app

[flash1293]

This only seems to happen when the height of the vega canvas is an even number.
Height 113px:

Height 114px:

[flash1293]

I can also reproduce this behaviour for 6.4