Convert path to string to avoid Graphiti::Errors::InvalidLink

[mkamensky]

The path argument to the method containing the line below is often a symbol, which causes the call to fail, eventually resulting in Graphiti raising Graphiti::Errors::InvalidLink. I suggest adding .to_s to path here.

https://github.com/graphiti-api/graphiti-rails/blame/759db8d25f14ae4b171e9b961e51ab50027a0d67/lib/graphiti/rails/railtie.rb#L134

[mkamensky]

Just saw that pull request #107 addresses it