Make capitalization of "Night theme" setting consistent with others

Been a pet peeve of mine for some time.

Author: triallax

app/src/main/res/values/strings.xml

@@ -69,7 +69,7 @@
     <string name="default_audio_format_title">Default audio format</string>
     <string name="default_video_format_title">Default video format</string>
     <string name="theme_title">Theme</string>
-    <string name="night_theme_title">Night Theme</string>
+    <string name="night_theme_title">Night theme</string>
     <string name="light_theme_title">Light</string>
     <string name="dark_theme_title">Dark</string>
     <string name="black_theme_title">Black</string>