dockerfile: use a newer version of Alpine

We see the "No space left on device" error on the current version,
so let's try to use a newer version of Alpine, maybe this error
has been fixed there.
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

scripts/build/Dockerfile.alpine

-FROM alpine:3.4
+FROM alpine:3.5
 ARG CC=gcc
 RUN apk update && apk add \
                 build-base \