Fix import that does not compile

Author: vietj

vertx-pg-client/src/test/java/io/vertx/pgclient/PgConnectionTest.java

@@ -21,6 +21,7 @@
 import io.vertx.ext.unit.TestContext;
 import io.vertx.sqlclient.ClosedConnectionException;
 import io.vertx.sqlclient.Row;
+import io.vertx.sqlclient.RowSet;
 import io.vertx.sqlclient.Tuple;
 import org.junit.Test;