Fix incorrect displayed default compression level in preferences

Author: VincidaB

src/Gui/PreferencePages/DlgSettingsDocument.ui

@@ -88,7 +88,7 @@
          <widget class="QLabel" name="textLabel1">
           <property name="text">
            <string>Document save compression level
-(0 = none, 9 = highest, 3 = default)</string>
+(0 = none, 9 = highest, 7 = default)</string>
           </property>
          </widget>
         </item>