Composer: move satooshi/php-coveralls to dev requirements

Author: petrkotek

composer.json

@@ -17,10 +17,10 @@
         }
     },
     "require": {
-        "php": "~5.3 || ^7.0",
-        "satooshi/php-coveralls": "^1.0"
+        "php": "~5.3 || ^7.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.8"
+        "phpunit/phpunit": "^4.8",
+        "satooshi/php-coveralls": "^1.0"
     }
 }