Remove a duplicated COPY directive

`COPY --from=build /usr/local/etc/gemrc /usr/local/etc` is called
twice, so this commit removes one of them.

Signed-off-by: moznion <[email protected]>

Author: moznion

Dockerfile

@@ -112,9 +112,6 @@ RUN set -ex && \
 
 RUN mkdir -p /usr/local/etc
 
-COPY --from=build \
-     /usr/local/etc/gemrc /usr/local/etc
-
 COPY --from=build \
      /usr/local/bin/bundle \
      /usr/local/bin/bundler \