test: mark test-repl-persistent-history as flaky

This test is already being investigated, but until a solution is found
it should be marked flaky.

Ref: #2319
Ref: #2356

PR-URL: #2659
Reviewed-By: orangemocha - Alexis Campailla <orangemocha@nodejs.org>

Author: joaocgreis

test/sequential/sequential.status

@@ -6,6 +6,7 @@ prefix sequential
 
 [true] # This section applies to all platforms
 test-child-process-fork-getconnections          : PASS,FLAKY
+test-repl-persistent-history                    : PASS,FLAKY
 
 [$system==win32]