Fix conda command for pytorch nightlies (#227)

Summary:
The location of the pytorch nightlies in conda has changed, this updates the installation script accordingly.
Pull Request resolved: #227

Test Plan: Tested locally with circleci cmd line + docker

Reviewed By: sdaulton

Differential Revision: D16737824

Pulled By: Balandat

fbshipit-source-id: 7e0c45ee003978b82da0563e167c30b2be604573

Author: Balandat

scripts/install_via_conda.sh

@@ -20,10 +20,10 @@ conda install -y conda-build
 
 if [[ $PYTORCH_NIGHTLY == true ]]; then
   # install CPU version for much smaller download
-  conda install -y -c pytorch pytorch-nightly-cpu
+  conda install -y -c pytorch-nightly pytorch cpuonly
 else
   # install CPU version for much smaller download
-  conda install -y -c pytorch pytorch-cpu
+  conda install -y -c pytorch pytorch cpuonly
 fi
 
 # get gpytorch master