Update README.md with correct go install path

[KenanHH]

Previous go install command will throw an error:

go: github.com/g-core/gcore-cli/cmd/gcore-cli@latest: version constraints conflict:
	github.com/g-core/gcore-cli@v0.1.1: parsing go.mod:
	module declares its path as: github.com/G-core/gcore-cli
	        but was required as: github.com/g-core/gcore-cli