Calrify imagegd2() synopsis

Although not quite as ambiguous as "GD", it's worth being clear that "GD2" is the name of the output format.

Author: IMSoP

reference/image/functions/imagegd2.xml

@@ -15,7 +15,7 @@
    <methodparam choice="opt"><type>int</type><parameter>mode</parameter><initializer><constant>IMG_GD2_RAW</constant></initializer></methodparam>
   </methodsynopsis>
   <para>
-   Outputs a GD2 image to the given <parameter>file</parameter>.
+   Outputs or saves the given <parameter>image</parameter> in GD2 format.
   </para>
  </refsect1>
  <refsect1 role="parameters">