Use Ctrl+Cmd+N shortcut for night mode

This matches iA Writer

writeas/Base.lproj/Main.storyboard

@@ -295,7 +295,8 @@ DQ
                                 <modifierMask key="keyEquivalentModifierMask"/>
                                 <menu key="submenu" title="View" id="HyV-fh-RgO">
                                     <items>
-                                        <menuItem title="Night Mode" keyEquivalent="u" id="jYO-0u-qN9">
+                                        <menuItem title="Night Mode" keyEquivalent="n" id="jYO-0u-qN9">
+                                            <modifierMask key="keyEquivalentModifierMask" control="YES" command="YES"/>
                                             <connections>
                                                 <action selector="toggleNightMode:" target="Voe-Tx-rLC" id="Nmq-eG-y3w"/>
                                             </connections>