[Maintenance][DX] Add var/ directory to gitignore (Sylius#419)

| Q               | A
| --------------- | -----
| Branch?         | 2.0
| Bug fix?        | no
| New feature?    | no
| Related tickets | -

Author: NoResponseMate

.gitignore

@@ -1,4 +1,5 @@
 /vendor/
+/var/
 /node_modules/
 /composer.lock