Update test syntax

test/syntax/syntax.md

@@ -44,6 +44,12 @@ h2
 
 ___
 
+- - -
+
+* * *
+
+_ _ _
+
 
 # List
 
@@ -505,6 +511,12 @@ var some: string = "typescript";
 - language: yaml
 ```
 
+```diff
+     not changed
+-    removed
++    added
+```
+
 
 # MathJax