Dot command not found when using constant

[sanderha]

Hey

When trying to run SilverGraph/png, it throws "Couldn't execute dot command, ensure graphviz is installed and 'dot' postpended to your graphviz path. See README.md. Shell error: sh: dot: command not found"

It does work however, if I manually enter the path to the dot exec, in the execute() method, instead of it being retrieved from a constant.

I have no idea why though, just thought I'd make you aware of it