Avoid stray '<!DOCTYPE>' text.

Avoid stray '<!DOCTYPE>' text.

The markdown converter converts the doctype header into html which
results in a stray line at the top of the chapter. This only affects
the chapters that still use markdown: Bash, Git, Command Line
Utilities, and Gridengine.

This patch applies a silly workaround. In the long run, the chapters
should be converted to plain html.