`upgrade`: handle app names case insensitively

[bevanjkay]

When running a mas upgrade command using an application name, the command is case-sensitive. This may be necessary, but if possible it would be nice for the commands to ignore case.

For example; Running mas upgrade spark does nothing. Running mas upgrade Spark completes the upgrade.

[chris-araman]

There's some overlap here with https://github.com/mas-cli/mas/issues/109.

I think the design here should follow Homebrew formula naming, where formula and cask names are all lowercase: https://docs.brew.sh/Formula-Cookbook#a-quick-word-on-naming

brew bundle interoperates with mas would allow users to install apps by name-token instead of (only) by integer ID.