Clean up specs and code

- don't use "should" in the spec example descriptions.
  e.g.:
    bad: it "should retriculate the splines"
    good: it "retriculates the splines"
- use parens to indicate whether a method call is a command or a query. No parens for commands; parens for queries
- spec subjects should come first
- use "described_class" when possible
- switch to 1-line blocks for let and subject blocks where possible
- reset the StackerBee::Client global configuration before each spec run instead of after