PHP7 compatible function definitions.

app/Models/Budget.php

@@ -3,6 +3,7 @@
 use Auth;
 use Crypt;
 use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
 use Illuminate\Database\Eloquent\SoftDeletes;
 use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
 
@@ -136,9 +137,9 @@ class Budget extends Model
     }
 
     /**
-     * @return \Illuminate\Database\Eloquent\Relations\BelongsTo
+     * @return BelongsTo
      */
-    public function user()
+    public function user(): BelongsTo
     {
         return $this->belongsTo('FireflyIII\User');
     }