Log Message:
Update to ruby-rgl to 0.5.2.

2016-05 Release 0.5.2

Horst Duchene <monora@gmail.com>
 * Issue #21: Use new method vertex_id instead of object_id to identify vertices \ 
in dot export. (fa7592)
 * Integrate Code Climate's test coverage reporting (0ab722)
 * Clarify traversal order of DFS search (see #20). (afa788)
Chase Gilliam <chase.gilliam@gmail.com>
 * drop 1.9.3 add newer jruby and rubinius (fad333)
Mat«¿as Battocchia <matias@riseup.net>
 * Switched to a different heap implementation. (bd7c13)
gorn <j@kub.cz>
 * Adding failing test for issue #24 (1f6204)