doc: fix typo in assert.md

PR-URL: #16866
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Vse Mozhet Byt <[email protected]>
Reviewed-By: Bryan English <[email protected]>

Author: mjomble

doc/api/assert.md

@@ -299,7 +299,7 @@ assert.fail(1, 2, 'whoops', '>');
 // AssertionError [ERR_ASSERTION]: whoops
 ```
 
-*Note*: Is the last two cases `actual`, `expected`, and `operator` have no
+*Note*: In the last two cases `actual`, `expected`, and `operator` have no
 influence on the error message.
 
 ```js