[FIX] multiline block parse

Hi,

With eyaml -i <file> containing multiline blocks I found the block was decrypted but on save left in that state.

Test:

eyaml -i test_input.yaml

change one of the blocks to include multiple lines, save and diff,
```
+    DEC(23)::PKCS7[the pink panther
+and some more]!
   - >
```
and the intermediary format is left behind in the saved file.