Use just the 'Parsoid/0.1' user agent so that we don't distort stats

We don't want to distort the browser stats at
http://stats.wikimedia.org/wikimedia/squids/SquidReportClients.htm, so don't
masquerade as Firefox.

Change-Id: I26349e7751368f943c1b5e07f98100f5715463a7