fix Lumen Documentation Address (#2501)

Author: SirousFakhri

docs/installation-lumen.md

@@ -5,7 +5,7 @@ weight: 5
 
 NOTE: Lumen is **not** officially supported by this package. However, the following are some steps which may help get you started.
 
-Lumen installation instructions can be found in the [Lumen documentation](https://lumen.laravel.com/docs/main).
+Lumen installation instructions can be found in the [Lumen documentation](https://lumen.laravel.com/docs/master).
 
 ## Installing