Correct possible invalid specified attributes

[raducoravu]

One of our end users had this Markdown table:

# XTRT
| Column 1 | Column 2 |
| --- | --- |
| Value 1 | Value 2 |
| Value 3 | Value 4 |
{: #table-id }

Notice that the user did not properly specify the attributes after the table:

  {: #table-id }

This ends up creating in com.elovirta.dita.markdown.renderer.AbstractRenderer.readAttributes(Title, AttributesBuilder) an attribute with name ":" and empty value and generates a not wellformed XML document.