bank-account: make last test quicker

exercises/bank-account/HINTS.md

@@ -4,5 +4,4 @@ To pass the last test you might find the
 
 Problems arising from running code concurrently are often intermittent because they depend on the order the code is
 executed. Therefore the last test runs many [threads](https://docs.oracle.com/javase/8/docs/api/java/lang/Thread.html) 
-several times to increase the chances of catching a bug. This means the last test might take a while to run, 
-though it shouldn't take more than a couple of minutes.
+several times to increase the chances of catching a bug.

exercises/bank-account/src/test/java/BankAccountTest.java

@@ -169,7 +169,7 @@ public class BankAccountTest {
         bankAccount.open();
         bankAccount.deposit(1000);
 
-        for (int i = 0; i < 1000; i++) {
+        for (int i = 0; i < 10; i++) {
             adjustBalanceConcurrently();
         }
     }