doc: fix typo in assert.md

PR-URL: #16866
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Bryan English <bryan@bryanenglish.com>

doc/api/assert.md

@@ -337,7 +337,7 @@ assert.fail(1, 2, new TypeError('need array'));
 // TypeError: need array
 ```
 
-*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