Update note error with syntax highlighting

[kukki]

Evernote plugin version: 0.1.1
Visual Studio Code version: 1.20.1
When there is a syntax highlighting block in the note, updating note will fail with error similar to:

Evernote Error: 11 - Attribute "class" must be declared for element type "code".

The syntax highlighting block is

<h1>To do</h1>
<h1>Done</h1>
<h1>Issue</h1>

After I remove xml, it works. But I lose highlighting feature.