Fix typo in comment

Co-authored-by: Dan Gohman <dev@sunfishcode.online>

Author: lukewagner

design/mvp/WIT.md

@@ -59,7 +59,7 @@ comment ::= '//' character-that-isnt-a-newline*
 ```
 
 There is a special type of comment called `documentation comment`. A
-`doc-comment` is either a line comment preceded with `///` whichends at the next
+`doc-comment` is either a line comment preceded with `///` which ends at the next
 newline (`\n`) character or it's a block comment which starts with `/**` and ends
 with `*/`. Note that block comments are allowed to be nested and their delimiters
 must be balanced