cleanup: Prefer template strings

Template strings are much nicer than string concatenation, so use
them where possible; this excludes translatable strings and any
strings containing '/' (until we can depend on gettext >= 0.20[0]).

[0] https://savannah.gnu.org/bugs/?50920

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/612

js/extensionPrefs/main.js

@@ -623,7 +623,7 @@ function initEnvironment() {
         },
 
         logError(s) {
-            log('ERROR: ' + s);
+            log(`ERROR: ${s}`);
         },
 
         userdatadir: GLib.build_filenamev([GLib.get_user_data_dir(), 'gnome-shell'])