Update rspec 'should' syntax to remove deprecation warnings

Use the new `:expect` syntax for RSpec to remove the following deprecation warnings:

```
Deprecation Warnings:

Using `should_receive` from rspec-mocks' old `:should` syntax without explicitly enabling the syntax is deprecated. Use the new
 `:expect` syntax or explicitly enable `:should` instead. Called from /Volumes/Mirego/hanzo/spec/cli/install_spec.rb:40:in `blo
ck (4 levels) in <top (required)>'.

Using `should` from rspec-expectations' old `:should` syntax without explicitly enabling the syntax is deprecated. Use the new 
`:expect` syntax or explicitly enable `:should` instead. Called from /Volumes/Mirego/hanzo/spec/cli/install_spec.rb:61:in `bloc
k (5 levels) in <top (required)>'.
```