[Bug] Execute python3 codes with 'python3 -filename.py' instead of 'python -filename.py'

- Code Runner Version: v0.12.2

**Bug description**
In many system using python3, to execute a python file 'python3 -filename.py' command is used in terminal/cmd instead of 'python -filename.py'. If we use 'python' it will show error.

**To Reproduce**

Check whether the system is showing error for 'python' command in terminal/cmd or not, if it is showing error, use 'python3', if still it's showing error, ask user to check Path variable or download python.