You need to either:
In addition to what dj_paige has posted and just to clarify.
Support for the Sony RX10 mk2 was introduced with Lr 6.1.1 and ACR 9.1.1. (to wit LR 6.1.1 has the equivalent processing engine as ACR 9.1.1)
Lightroom 5.7 has the equivalent of ACR 8.7. (there is no option to use ACR 9.1.1 in Lightroom 5.7)
See the link below for further details.