Update composer.json

restrict the use of lib-curl 7.35 in order to avoid "Problem (2) in the Chunked-Encoded data" described here: https://github.com/jackalope/jackalope-jackrabbit/issues/89
i would rather add this as 
```
"conflict": {
    "lib-curl" : "7.35"
}
```
https://getcomposer.org/doc/04-schema.md#conflict