Fix cannot parse multi JOIN expressions

[git-hulk]

This closes #55

[coveralls]

Pull Request Test Coverage Report for Build 8140062777

Details

• 93 of 122 (76.23%) changed or added relevant lines in 3 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.2%) to 57.118%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
parser/ast_visitor.go	3	5	60.0%
parser/ast.go	41	53	77.36%
parser/parser_query.go	49	64	76.56%

Files with Coverage Reduction	New Missed Lines	%
parser/parser_query.go	2	60.87%

Totals
Change from base Build 8074699257:	0.2%
Covered Lines:	5541
Relevant Lines:	9701

---

💛 - Coveralls