Update installation.rst (#1746)
Update installation.rst (#1746)

according to `nix-shell`:
```
error: 'opencl-icd' has been renamed to/replaced by 'ocl-icd'
```
diku-dk/futhark,diku-dk/futhark,diku-dk/futhark,diku-dk/futhark,diku-dk/futhark