circleci-cli/install doesn't install the circleci tool

### Orb version

0.1.9

### What happened

The `src/scripts/install.sh` script simply doesn't install the CLI tool if it's missing.
It only does things if it already exists:
- either the installed version is the version we want, and it does nothing
- either it install a different version

But it expects the CLI tool to be already present, which seems wrong.

### Expected behavior

If `circleci` is not available, I would expect it to install the tool with the provided version