only upgrade packages in the user's home folder

[robinpaulson]

i'd like to have an option which only upgrades those packages in ~/.local/

if i run the script at present, it upgrades all the scripts which are controlled by the package manager, apt. that then breaks other packages which require specific versions.

i'll take a look later, see if i can put together a PR

thanks

[robinpaulson]

Perhaps #4 fixes this?