default.rst: Added empty comment after directives.

This prevents a subsequent indented paragraph from being captured
by the directive.  Closes pandoc#321.

default.rst

@@ -18,6 +18,7 @@ $endif$
 $if(math)$
 .. role:: math(raw)
    :format: html latex
+..
 
 $endif$
 $for(include-before)$
@@ -26,6 +27,7 @@ $include-before$
 $endfor$
 $if(toc)$
 .. contents::
+..
 
 $endif$
 $for(header-includes)$