Change 'normal' to 'standard'

Use better wording in this sentence.

doc/user/asciidoc.md

@@ -495,7 +495,7 @@ video::movie.mp4[width=640,start=60,end=140,options=autoplay]
 ```
 
 GitLab does not support embedding YouTube and Vimeo videos in AsciiDoc content.
-Use a normal AsciiDoc link:
+Use a standard AsciiDoc link:
 
 ```plaintext
 https://www.youtube.com/watch?v=BlaZ65-b7y0[Link text for the video]