Install method "GO" not updated and doesn't work as it is currently in README.md

[jaysonng]

the new line of code should be

go install github.com/back4app/parse-cli@latest

instead of what is it is currently

go get -t github.com/back4app/parse-cli

as this produces the error:

'go get' is no longer supported outside a module.
	To build and install a command, use 'go install' with a version,
	like 'go install example.com/cmd@latest'
	For more information, see https://golang.org/doc/go-get-install-deprecation
	or run 'go help get' or 'go help install'.

[charles-ramos]

Thank you, the readme is updated here: #38