Accept '-' in usernames for ls self-test

[jas4711]

Hi! We got this test failure because - is not accepted in usernames by the code, this pull request fixes this.

=== RUN   TestRunLsWithExamplesDirectoryWithOSLookup
    ls_formatting_test.go:87: drwxr-xr-x    8 salsa-ci users        4096 Oct 7 13:16 examples
    ls_formatting_test.go:138: runLs("examples"): username / uid mismatch, expected user, got: "salsa-ci", err: <nil>
--- FAIL: TestRunLsWithExamplesDirectoryWithOSLookup (0.00s)
=== RUN   TestRunLsWithLicensesFileWithOSLookup
    ls_formatting_test.go:87: -rw-r--r--    1 salsa-ci users        1289 Oct 7 13:16 LICENSE
    ls_formatting_test.go:138: runLs("LICENSE"): username / uid mismatch, expected user, got: "salsa-ci", err: <nil>
--- FAIL: TestRunLsWithLicensesFileWithOSLookup (0.00s)

Thanks,
Simon

[puellanivis]

If we’re going to be expanding this username regexp, then we should probably target adding all the allowed characters (that is, underscore and period) and upper-case letters.

[jas4711]

I updated the pull request to include those in the regexp too, thanks!