Update dependencies and a few style cleanups

This updates to the latest Assert. This ensures we are using the
latest assert with the latest features. This also includes a few
cleanups. This changes from rescueing `Exception` to
`StandardError` which is a better practice. This also ensures in
the tests that we are stubbing the `TCPServer` module that DatTCP
defines instead of defining the one provided by ruby. Finally,
this changes the `BaseTests` to `UnitTests` per our latest
conventions. This is all part of keeping DatTCP up-to-date with
our latest standards and conventions.