Conda: Add numpy dependency (#4442)

`import torchvision` fails if numpy is not installed, so it should have
an explicit dependency on it (which is already the case for wheel
package)

packaging/torchvision/meta.yaml

@@ -22,6 +22,7 @@ requirements:
 
   run:
     - python
+    - defaults::numpy >=1.11
     - libpng
     - ffmpeg >=4.2  # [not win]
     - jpeg