rotated log files with correct file extension

[CodiePP]

it's difficult for Windows to open the correct program to display log files (JSON or text) if the extension is missing on the file name.

examples: Daedalus.json-20190826193801 or node.json-20190904210955

=> the filename stem should not contain the extension, log rotator adds the timestamp and then the extension

[CodiePP]

the filename now looks like this: node-20190904210955.json
and thus Windows should open it with the program that is associated to the extension .json