Fix the error of val2017_foot training

[Galaxies99]

1. When running foot validation dataset v1, the Matlab code crash because of wrong number of joints. (the json data has only 6 joints while the code says 23). The solution may be helpful to Issue #16 .

2. Foot dataset v2 not available yet, so change it to dataset v1, which may solve the Issue #12 , #22 .

Thanks.

[gineshidalgo99]

Thanks!