Update facade docblocks

Author: taylorotwell

src/Illuminate/Support/Facades/Schema.php

@@ -31,6 +31,7 @@
  * @method static void drop(string $table)
  * @method static void dropIfExists(string $table)
  * @method static void dropColumns(string $table, string|array $columns)
+ * @method static void dropColumnsIfExists(string $table, string|array $columns)
  * @method static void dropAllTables()
  * @method static void dropAllViews()
  * @method static void dropAllTypes()