appendToPATH method
Appends path
to the end of the PATH
in a persistent manner.
Note: this doesn't update current scripts
path.
Returns true if we successfully appended the path.
In almost all shells you will need to restart
the terminal in order for the path change to take affect.
Implementation
@override
bool appendToPATH(String path) =>
throw UnsupportedError('Not supported in sh');