Fix missing cipher on file decryption (#26)

Currently if a file was encrypted with any cipher other than the default, decryption would fail.

Author: marcqualie

lib/diffcrypt/file.rb

@@ -34,10 +34,11 @@ def encrypt(key, cipher: DEFAULT_CIPHER)
       Encryptor.new(key, cipher: cipher).encrypt(read)
     end
 
+    # TODO: Add a test to verify this does descrypt properly
     def decrypt(key)
       return read unless encrypted?
 
-      Encryptor.new(key).decrypt(read)
+      Encryptor.new(key, cipher: cipher).decrypt(read)
     end
 
     def to_yaml