Before this commit, t-raw a string containing `<svg>` did not display
the svg element. This was because of missing namespace in vnode's data.
Now, `vdom.addNS` is called to add the svg namespace when necessary.
Before this commit, a condition deemed always true made
the building crash. The happened with TypeScript == 3.7.2
After this commit, the required typescript version has been
changed, as well as the incriminated true condition