Add composer dependency on base theme.

composer.json

@@ -12,6 +12,9 @@
       "url": "https://packages.drupal.org/8"
     }
   ],
+  "require": {
+    "roblib/magazineplus_lmmi_journal": "dev-master"
+  },
   "license": "GPL-2.0-or-later",
   "authors": [
     {