Support Laravel < 6 for Illuminate\Support\Env usage (mcamara#750)

* Use Env::get instead of env

It conflicts with other `env()` global functions (such as CakePHP), and most of them don't handle closures.

* Support Laravel < 6 for Illuminate\Support\Env usage

Fixed `env()` and `Illuminate\Support\Env` usage to support Laravel < 6

src/Mcamara/LaravelLocalization/LaravelLocalization.php

@@ -1037,12 +1037,22 @@ protected function normalizeAttributes($attributes)
      */
     protected function getForcedLocale()
     {
-        return Env::get(static::ENV_ROUTE_KEY, function () {
-            $value = getenv(static::ENV_ROUTE_KEY);
+        if (version_compare($this->app->version(), '6') >= 0) {
+            return Env::get(static::ENV_ROUTE_KEY, function () {
+                $value = getenv(static::ENV_ROUTE_KEY);
 
-            if ($value !== false) {
-                return $value;
-            }
-        });
+                if ($value !== false) {
+                    return $value;
+                }
+            });
+        } else {
+            return env(static::ENV_ROUTE_KEY, function () {
+                $value = getenv(static::ENV_ROUTE_KEY);
+
+                if ($value !== false) {
+                    return $value;
+                }
+            });
+        }
     }
 }