Consistently use Dpkg::Progress* in documentation

Closes: 745452

doc/apt-get.8.xml

@@ -536,7 +536,7 @@
      terminal window when packages are installed, upgraded or
      removed. For a machine parsable version of this data see
      README.progress-reporting in the apt doc directory.
-     Configuration Item: <literal>DpkgPM::Progress</literal> and <literal>Dpkg::Progress-Fancy</literal>.</para></listitem>
+     Configuration Item: <literal>Dpkg::Progress</literal> and <literal>Dpkg::Progress-Fancy</literal>.</para></listitem>
      </varlistentry>