docs: update quote constants

Author: alexkart

README.md

@@ -113,10 +113,10 @@ Quoting character can be changed to double quote or removed
 ```php
 $command->addOption('-d', 'data1');
 $command->addOption('-d', 'data"2');
-$command->setQuoteCharacter(Command::QUOTE_CHARACTER_DOUBLE);
+$command->setQuoteCharacter(Command::QUOTE_DOUBLE);
 // curl -d "data" -d "data\"2"
 
 $command->addOption('-d', 'data');
-$command->setQuoteCharacter(Command::QUOTE_CHARACTER_NONE);
+$command->setQuoteCharacter(Command::QUOTE_NONE);
 // curl -d data
 ```