Fix delimiter row matching pattern for tables (dart-lang/markdown#540)

pkgs/markdown/lib/src/patterns.dart

diff --git a/pkgs/markdown/lib/src/patterns.dart b/pkgs/markdown/lib/src/patterns.dart
index 68299ee..967434a 100644
--- a/pkgs/markdown/lib/src/patterns.dart
+++ b/pkgs/markdown/lib/src/patterns.dart
@@ -48,7 +48,7 @@
 
 /// A line of hyphens separated by at least one pipe.
 final tablePattern = RegExp(
-    r'^[ ]{0,3}\|?([ \t]*:?\-+:?[ \t]*\|)+([ \t]|[ \t]*:?\-+:?[ \t]*)?$');
+    r'^[ ]{0,3}\|?([ \t]*:?\-+:?[ \t]*\|[ \t]*)+([ \t]|[ \t]*:?\-+:?[ \t]*)?$');
 
 /// A line starting with `[^` and contains with `]:`, but without special chars
 /// (`\] \r\n\x00\t`) between. Same as [GFM](cmark-gfm/src/scanners.re:318).

pkgs/markdown/test/extensions/tables.unit

diff --git a/pkgs/markdown/test/extensions/tables.unit b/pkgs/markdown/test/extensions/tables.unit
index 482ef12..35b1a15 100644
--- a/pkgs/markdown/test/extensions/tables.unit
+++ b/pkgs/markdown/test/extensions/tables.unit
@@ -336,3 +336,22 @@
 <p>| A | <a href="url">B</a> | C |
 |---|---|
 |  a | b | c |</p>
+>>> trailing whitespace after delimiter row
+| Name    | Value |
+| ---     | ---   |     
+| Foo     | bar   |
+<<<
+<table>
+<thead>
+<tr>
+<th>Name</th>
+<th>Value</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td>Foo</td>
+<td>bar</td>
+</tr>
+</tbody>
+</table>