LP#1857710: fix Angular client whitescreen on Firefox

LP#1857710: fix Angular client whitescreen on Firefox

Work done for LP#1830391 added an instance of a Javascript
regexp replace using the dotAll ("/s") flag, but as of the moment
Firefox treats that flag as a fatal syntax error, breaking the
Angular staff client.

To test
-------
[1] Attempt to log in the Angular staff client with Firefox. Note
    that you get a whitescreen with the following in the browser
    console:

    SyntaxError: invalid regular expression flag s
[2] Apply the patch and repeat step 1. This time, the Angular
    staff client should work normally.
[3] Verify that the Angular unit tests pass.

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>