Add extra fixture

Related to: remarkjs/remark#678.

Author: wooorm

test/previous.html

@@ -35,3 +35,7 @@ <h2>Others characters before</h2>
 github.com: !<a href="mailto:a@b.c">a@b.c</a>, "<a href="mailto:a@b.c">a@b.c</a>, #<a href="mailto:a@b.c">a@b.c</a>, $<a href="mailto:a@b.c">a@b.c</a>, &amp;<a href="mailto:a@b.c">a@b.c</a>, '<a href="mailto:a@b.c">a@b.c</a>, )<a href="mailto:a@b.c">a@b.c</a>, <a href="mailto:+a@b.c">+a@b.c</a>,
 ,<a href="mailto:a@b.c">a@b.c</a>, <a href="mailto:-a@b.c">-a@b.c</a>, <a href="mailto:.a@b.c">.a@b.c</a>, /a@b.c, :<a href="mailto:a@b.c">a@b.c</a>, ;<a href="mailto:a@b.c">a@b.c</a>, &lt;<a href="mailto:a@b.c">a@b.c</a>, =<a href="mailto:a@b.c">a@b.c</a>, ><a href="mailto:a@b.c">a@b.c</a>, ?<a href="mailto:a@b.c">a@b.c</a>,
 @<a href="mailto:a@b.c">a@b.c</a>, \<a href="mailto:a@b.c">a@b.c</a>, ]<a href="mailto:a@b.c">a@b.c</a>, ^<a href="mailto:a@b.c">a@b.c</a>, `<a href="mailto:a@b.c">a@b.c</a>, {<a href="mailto:a@b.c">a@b.c</a>, }<a href="mailto:a@b.c">a@b.c</a>.</p>
+<h2>remarkjs/remark#678</h2>
+<p>,<a href="https://github.com">https://github.com</a></p>
+<p>[ ,<a href="https://github.com">https://github.com</a></p>
+<p>[asd] ,<a href="https://github.com">https://github.com</a></p>

test/previous.md

@@ -64,3 +64,11 @@ While other characters before the email aren’t allowed by GFM, they work on
 github.com: !a@b.c, "a@b.c, #a@b.c, $a@b.c, &a@b.c, 'a@b.c, )a@b.c, +a@b.c,
 ,a@b.c, -a@b.c, .a@b.c, /a@b.c, :a@b.c, ;a@b.c, <a@b.c, =a@b.c, >a@b.c, ?a@b.c,
 @a@b.c, \a@b.c, ]a@b.c, ^a@b.c, `a@b.c, {a@b.c, }a@b.c.
+
+## remarkjs/remark#678
+
+,https://github.com
+
+[ ,https://github.com
+
+[asd] ,https://github.com