spellcheck: fix default language value

The default value was set to "None" in appsettingsmanager.h but the rest
of the code assumes that the default is "NONE" (see commit 2a72da56).

GitLab: #1997
Change-Id: Ifeac3399b1b48bad0863a1b7da9228df43f73b76

src/app/appsettingsmanager.h

@@ -63,7 +63,7 @@ extern const QString defaultDownloadPath;
     X(WindowState, QWindow::AutomaticVisibility) \
     X(EnableExperimentalSwarm, false) \
     X(LANG, "SYSTEM") \
-    X(SpellLang, "None") \
+    X(SpellLang, "NONE") \
     X(EnableSpellCheck, true) \
     X(PluginStoreEndpoint, "https://plugins.jami.net") \
     X(PositionShareDuration, 15) \