When calling toString on subjoin with joins, the result is not as expected

[tomershay]

For this query:
SELECT COUNT(DISTINCT tbl1.id) FROM (tbl1, tbl2, tbl3)
When parsing and deparsing, the output is:
SELECT COUNT(DISTINCT tbl1.id) FROM (tbl1 tbl2 tbl3)
Note the missing commas between the table names in the FROM clause.

This pull request fixes that issue.

[coveralls]

Coverage increased (+0.007%) to 83.973% when pulling 47457ed on tomershay:subjoin_with_joins_issue into d9025e8 on JSQLParser:master.