Add a little bit more whitespace removal by trimming.

[rodrigoaguilera]

When a svg with whitespaces or linebreaks at the end is passed those are preserved. I thought it would be better to remove them

[rodrigoaguilera]

I forgot to mention that when you sanitize a file with no newline at the end the process adds an unnecessary newline to the output. I think is a bug in libxml.

For me this generates a diff between the sanitized and unsanitized version of the file that I hope it can be solved upstream.