Bump maatwebsite/excel from 2.1.x-dev to 3.1.x-dev

Bumps [maatwebsite/excel](https://github.com/Maatwebsite/Laravel-Excel) from 2.1.x-dev to 3.1.x-dev.
- [Release notes](https://github.com/Maatwebsite/Laravel-Excel/releases)
- [Commits](https://github.com/Maatwebsite/Laravel-Excel/commits)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

composer.json

@@ -19,7 +19,7 @@
   "require": {
     "php": ">=5.5.9",
     "illuminate/support": "*",
-    "maatwebsite/excel": "~2.1.0"
+    "maatwebsite/excel": "~3.1.x-dev"
   },
   "autoload": {
     "psr-4": {