Cast JWT_TTL value to integer in config.php if sourced from environm…

…ent variable

The env file is passing values as string and if manually the developer set the JWT_TTL value in the env file an error of : 
```
Carbon\\Carbon::rawAddUnit(): Argument tymondesigns#3 ($value) must be of type int|float, string given,
```
will appear

Fixes tymondesigns#2256

config/config.php

@@ -101,7 +101,7 @@
     |
     */
 
-    'ttl' => env('JWT_TTL', 60),
+    'ttl' => (int) env('JWT_TTL', 60),
 
     /*
     |--------------------------------------------------------------------------