fix(gfmCodeBlocks): allow the info string in gfmCodeBlocks to contain spaces

The line with the opening code fence may optionally contain some text following the code fence (the info string); this is trimmed of leading and trailing whitespace and can contain multiple words (but not newlines).

Closes #856

src/subParsers/makehtml/githubCodeBlocks.js

@@ -20,9 +20,13 @@ showdown.subParser('makehtml.githubCodeBlocks', function (text, options, globals
 
   text += '¨0';
 
-  text = text.replace(/(?:^|\n)(?: {0,3})(```+|~~~+)(?: *)([^\s`~]*)\n([\s\S]*?)\n(?: {0,3})\1/g, function (wholeMatch, delim, language, codeblock) {
+  text = text.replace(/(?:^|\n) {0,3}(```+|~~~+) *([^\n\t`~]*)\n([\s\S]*?)\n {0,3}\1/g, function (wholeMatch, delim, language, codeblock) {
     var end = (options.omitExtraWLInCodeBlocks) ? '' : '\n';
 
+    // if the language has spaces followed by some other chars, according to the spec we should just ignore everything
+    // after the first space
+    language = language.trim().split(' ')[0];
+
     // First parse the github code block
     codeblock = showdown.subParser('makehtml.encodeCode')(codeblock, options, globals);
     codeblock = showdown.subParser('makehtml.detab')(codeblock, options, globals);

test/functional/makehtml/cases/issues/#856.gfm-codeblock-with-language-with-spaces.html

@@ -0,0 +1,8 @@
+<pre><code class="json language-json">{
+    "custom": true
+}
+</code></pre>
+<pre><code class="json language-json">{
+    "custom": false
+}
+</code></pre>

test/functional/makehtml/cases/issues/#856.gfm-codeblock-with-language-with-spaces.md

@@ -0,0 +1,11 @@
+```json custom data
+{
+    "custom": true
+}
+```
+
+```json custom data
+{
+    "custom": false
+}
+```