PHP-CS-Fixer should stay as a dev dependency

Closes #236
Closes #237

composer.json

@@ -36,15 +36,15 @@
         "ext-xml": "*",
         "ext-xmlwriter": "*",
         "ext-zip": "*",
-        "psr/simple-cache": "^1.0",
-        "friendsofphp/php-cs-fixer": "^2.7"
+        "psr/simple-cache": "^1.0"
     },
     "require-dev": {
         "tecnickcom/tcpdf": "^6.2",
         "squizlabs/php_codesniffer": "^2.7",
         "phpunit/phpunit": "^5.7",
         "dompdf/dompdf": "^0.8.0",
-        "mpdf/mpdf": "7.0.0-RC1@dev"
+        "mpdf/mpdf": "7.0.0-RC1@dev",
+        "friendsofphp/php-cs-fixer": "^2.7"
     },
     "suggest": {
         "ext-gd": "Required for exact column width autocalculation",