fix(tables): fix table heading separators requiring 3 dashes instead of 2

Closes #256

Author: Estevão Soares dos Santos

dist/showdown.js

@@ -5,14 +5,14 @@ showdown.subParser('tables', function (text, options, globals) {
     return text;
   }
 
-  var tableRgx = /^[ \t]{0,3}\|?.+\|.+\n[ \t]{0,3}\|?[ \t]*:?[ \t]*(?:-|=){3,}[ \t]*:?[ \t]*\|[ \t]*:?[ \t]*(?:-|=){3,}[^]+?(?:\n\n|~0)/gm;
+  var tableRgx = /^[ \t]{0,3}\|?.+\|.+\n[ \t]{0,3}\|?[ \t]*:?[ \t]*(?:-|=){2,}[ \t]*:?[ \t]*\|[ \t]*:?[ \t]*(?:-|=){2,}[^]+?(?:\n\n|~0)/gm;
 
   function parseStyles(sLine) {
-    if (/^:[ \t]*---*$/.test(sLine)) {
+    if (/^:[ \t]*--*$/.test(sLine)) {
       return ' style="text-align:left;"';
-    } else if (/^---*[ \t]*:[ \t]*$/.test(sLine)) {
+    } else if (/^--*[ \t]*:[ \t]*$/.test(sLine)) {
       return ' style="text-align:right;"';
-    } else if (/^:[ \t]*---*[ \t]*:$/.test(sLine)) {
+    } else if (/^:[ \t]*--*[ \t]*:$/.test(sLine)) {
       return ' style="text-align:center;"';
     } else {
       return '';

dist/showdown.js.map

@@ -0,0 +1,14 @@
+<table>
+    <thead>
+    <tr>
+        <th>key</th>
+        <th>value</th>
+    </tr>
+    </thead>
+    <tbody>
+    <tr>
+        <td>My Key</td>
+        <td>My Value</td>
+    </tr>
+    </tbody>
+</table>

dist/showdown.min.js

@@ -0,0 +1,3 @@
+|key|value|
+|--|--| 
+|My Key|My Value|