Spelling error

Changed ciper to cipher

Author: Nawfay

README.md

@@ -68,7 +68,7 @@ const cipher = await aes.encrypt("This is AES-128-CBC. It works.");
 console.log(cipher.hex());
 // 41393374609eaee39fbe57c96b43a9da0d547c290501be50f983ecaac6c5fd1c
 
-const plain = await aes.decrypt(ciper);
+const plain = await aes.decrypt(cipher);
 console.log(plain.toString());
 // This is AES-128-CBC. It works.
 ```