tree_generator: replace - with _ for tree node parameters in .json file

[angeltop]

tree_generator behavior is as expected, tree node execution is the desired one. One minor bug found in the creation of .json files, where "-" was not replaced with "_". This is the fix. Thank you Diogo and I apologize for the delay. :)

[diogoalmeida]

Thanks! I will then merge the changes in the master branch and mark #6 and #7 as solved.

If you do plan to pass more parameters from the keyframes, the changes to the code should be minor, but there will need to be some changes, so please contact me in that eventuality.