Apply suggestions from code review

Co-authored-by: Sindre Sorhus <[email protected]>

Author: Mesteery

docs/rules/prefer-t-throws.md

@@ -9,10 +9,10 @@ const test = require('ava');
 
 test('some test', async t => {
 	try {
-		await Promise.reject('error');
+		await potentiallyThrowingFunction();
 		t.fail();
 	} catch (error) {
-		t.is(error, 'error');
+		t.is(error.message, 'Unicorn overload');
 	}
 });
 ```
@@ -57,4 +57,3 @@ test('some test', async t => {
 	}
 });
 ```
-