Allow tildes in info string of a fence block with tilde marker

This is now allowed as per commonmark 0.29 spec:
~~~ js ~~~
console.log('hello, world!');
~~~

See also:
b7651e4f8b

lib/rules_block/fence.js

@@ -31,7 +31,11 @@ module.exports = function fence(state, startLine, endLine, silent) {
   markup = state.src.slice(mem, pos);
   params = state.src.slice(pos, max);
 
-  if (params.indexOf(String.fromCharCode(marker)) >= 0) { return false; }
+  if (marker === 0x60 /* ` */) {
+    if (params.indexOf(String.fromCharCode(marker)) >= 0) {
+      return false;
+    }
+  }
 
   // Since start is found, we can report success here in validation mode
   if (silent) { return true; }

test/fixtures/commonmark/bad.txt

@@ -15,25 +15,6 @@ error:
 aaa</p>
 
 
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-src line: 1995
-
-.
-~~~ aa ``` ~~~
-foo
-~~~
-.
-<pre><code class="language-aa">foo
-</code></pre>
-.
-
-error:
-
-<p>~~~ aa ``` ~~~
-foo</p>
-<pre><code></code></pre>
-
-
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 src line: 5176
 

test/fixtures/commonmark/good.txt

@@ -1473,6 +1473,18 @@ foo
 foo</p>
 .
 
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+src line: 1995
+
+.
+~~~ aa ``` ~~~
+foo
+~~~
+.
+<pre><code class="language-aa">foo
+</code></pre>
+.
+
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 src line: 2007
 

test/fixtures/markdown-it/commonmark_extras.txt

@@ -190,16 +190,6 @@ bar
 </ul>
 .
 
-Info string in fenced code block can't contain marker used for the fence
-.
-~~~test~
-
-~~~test`
-.
-<p>~~~test~</p>
-<pre><code class="test`"></code></pre>
-.
-
 Tabs should be stripped from the beginning of the line
 .
  foo