Merge pull request #7 from SolumDeSignum/dev

1.) reverted: back wrong funciality we are not using DeferrableProvider

src/InvoicesServiceProvider.php

@@ -4,10 +4,9 @@
 
 namespace SolumDeSignum\Invoices;
 
-use Illuminate\Contracts\Support\DeferrableProvider;
 use Illuminate\Support\ServiceProvider;
 
-class InvoicesServiceProvider extends ServiceProvider implements DeferrableProvider
+class InvoicesServiceProvider extends ServiceProvider
 {
     /**
      * Perform post-registration booting of services.