Make option for diff viewer in git options clearer

Change-Id: Iae0f427ed447430c82852c967022bc30ee4e88d1
Reviewed-by: Jarek Kobus <jaroslaw.kobus@digia.com>

src/plugins/git/settingspage.ui

@@ -140,7 +140,7 @@
       <item row="2" column="3">
        <widget class="QCheckBox" name="useDiffEditorCheckBox">
         <property name="text">
-         <string>Use Diff Editor</string>
+         <string>Show diff side-by-side</string>
         </property>
        </widget>
       </item>