remove unused dotenv library from dev dependencies

composer.json

@@ -9,8 +9,7 @@
     "require-dev": {
         "mockery/mockery": "^1.1",
         "phpunit/phpunit": "^7.2",
-        "squizlabs/php_codesniffer": "^3.3",
-        "symfony/dotenv": "^4.1"
+        "squizlabs/php_codesniffer": "^3.3"
     },
     "autoload": {
         "psr-4": {