Update Alpine Linux to 3.12 (#157)

Dockerfile

@@ -5,7 +5,7 @@ RUN go mod download
 ADD . /csi/
 RUN CGO_ENABLED=0 go build -o driver.bin github.com/hetznercloud/csi-driver/cmd/driver
 
-FROM alpine:3.10
+FROM alpine:3.12
 RUN apk add --no-cache ca-certificates e2fsprogs xfsprogs blkid xfsprogs-extra e2fsprogs-extra
 COPY --from=builder /csi/driver.bin /bin/hcloud-csi-driver
 ENTRYPOINT ["/bin/hcloud-csi-driver"]