Fix Conda CI (#1884)

Summary:
Currently CI jobs using conda are failed due to conflict packages.
This PR fixes this.

- use newer `numpy` to build `faiss-cpu`
- install `pytorch` when testing `faiss-cpu`
    - to find correct `pytorch` package, `pytorch` channel is set at `conda build`

Pull Request resolved: https://github.com/facebookresearch/faiss/pull/1884

Reviewed By: mdouze

Differential Revision: D28777447

Pulled By: beauby

fbshipit-source-id: 82a1ce076abe6bbbba9415e8935ed57b6104b6c3

.circleci/config.yml

@@ -93,9 +93,8 @@ jobs:
           name: Conda build
           command: |
             conda install -y -q conda-build
-            conda install -c pytorch pytorch
             cd conda
-            conda build faiss --python 3.7
+            conda build faiss --python 3.7 -c pytorch
 
   build_osx:
     macos:
@@ -158,9 +157,8 @@ jobs:
           name: Build/test
           command: |
             conda install conda-build
-            conda install -c pytorch pytorch
             cd conda
-            conda build faiss --python 3.7
+            conda build faiss --python 3.7 -c pytorch
 
   build_linux_gpu:
     machine: