Fix for #122. Add Pester test for Pretty.

fix for https://github.com/adamdriscoll/poshtools/issues/122

This fix issue for item with ```.``` or ```&``` will change to item in "$(Get-Alias)".

Also added Pester test.
All Test will pass with https://github.com/adamdriscoll/poshtools/pull/123 is merged. If not merged, Test for PSCustomObject will be failed.