fix broken url

Please refer to issue #637

src/content/contributor-docs/en/documentation_style_guide.mdx

@@ -70,7 +70,7 @@ Please use American English (color, center, modularize, etc). See [a list of Ame
 
 ## Oxford Comma
 
-Please use the [Oxford comma](https://en.wikipedia.org/wiki/Serial_comma/) ("red, white, and blue", instead of "red, white and blue").
+Please use the [Oxford comma](https://en.wikipedia.org/wiki/Serial_comma) ("red, white, and blue", instead of "red, white and blue").
 
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