file:// URLs not rendered as links

[juris-greitans]

To reproduce, create and open a file with following contents (I'm using a Windows computer):

[This should  be a link](file:///C:/test.md)

The contents are not rendered, no link appears.

Although (as inspired by #225 ;-)), when omitting the protocol part file://, the link is rendered correctly:

[This should  be a link](/C:/test.md)