Prefer short symbol key syntax over hash rockets

It makes the code cleaner and easier to read.
Update examples to obey rule for percent literals

Update examples using parentheses (`()`) to use square brackets (`[]`)
in order to not break rule "Prefer `[]` as delimiters for all `%`
literals".
Do not rely on hashes being ordered since 1.9

Hashes in general are often thought of as begin unordered. An
implementation that relies on the fact that a Ruby hash since 1.9
retains the order of its keys can be a source of confusion.
Update string interpolation examples to obey rule

Update examples so that they do not break the rule "Use `{}` around
instance variables being interpolated into a string".
Fix formatting and typo