Install classy-vision by default in torchelastic/… (#14)

Summary:
Valiated docker build

```
VERSION=0.1.0.dev1
docker build -t torchelastic/examples:$VERSION . --build-arg BASE_IMAGE=pytorch/elastic:$VERSION
```
Pull Request resolved: #14

Differential Revision: D18824375

Pulled By: kiukchung

fbshipit-source-id: eb731e72012cea8ad8c0ed54b835097de5c4ab55

Author: Kiuk Chung

examples/Dockerfile

@@ -5,12 +5,7 @@ ARG WITH_CLASSY_VISION=1
 
 # install utilities and dependencies
 RUN pip install awscli --upgrade
-
-RUN if [ "$WITH_CLASSY_VISION" = "1" ]; then \
-      pip install classy-vision
-    else \
-      echo "building without ClassyVision" ; \
-    fi
+RUN pip install classy-vision
 
 WORKDIR /workspace
 COPY . ./examples