When running rbt alias --dry-run on a system command alias (an alias

that executes a command, marked with a leading !), the result would be

a list of characters separated by spaces.
This was due to a bad assumption in the code where we assumed the value

we were working with was a list, each representing part of a command

invocation. These sorts of aliases were represented as a string, so we

ended up treating the string as a list of individual characters,

inserting spaces between each.
This change fixes this bug buy only attempting this normalization if

working with a list. Strings are printed as-is.

Tested with both types of aliases. Saw the expected results.
Tested the links in the new release notes.