Fix: Use number

Author: localheinz

README.md

@@ -140,7 +140,7 @@ Detected 11 tests that took longer than expected.
 0.802 (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Default\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithDataProvider#1
 0.703 (0.500) Ergebnis\PHPUnit\SlowTestDetector\Test\EndToEnd\Default\SleeperTest::testSleeperSleepsLongerThanDefaultMaximumDurationWithDataProvider#0
 
-There is one additional slow test that is not listed here.
+There is 1 additional slow test that is not listed here.
 
 Time: 00:12.601, Memory: 8.00 MB