Dockerfile: update & upgrade & remove build files

Signed-off-by: Terekhin Alexandr <alex@bearns.me>

Dockerfile

@@ -1,5 +1,6 @@
 FROM alpine:latest
-RUN apk add --no-cache openssl-dev linux-headers zlib-dev gcc gperf cmake build-base git libstdc++ \
+RUN apk update && apk --no-cache upgrade \
+	&& apk add --no-cache openssl-dev linux-headers zlib-dev gcc gperf cmake build-base git libstdc++ \
 	&& git clone --recursive https://github.com/tdlib/telegram-bot-api.git \
 	&& cd telegram-bot-api \
 	&& mkdir build \
@@ -7,6 +8,7 @@ RUN apk add --no-cache openssl-dev linux-headers zlib-dev gcc gperf cmake build-
 	&&	cmake -DCMAKE_BUILD_TYPE=Release .. \
 	&& cmake --build . -j 4 --target install \
 	&& apk del linux-headers gcc gperf cmake build-base git \
+	&& cd ../.. \
 	&& rm -r ./telegram-bot-api
 RUN adduser --no-create-home --uid 2000 --disabled-password tg-bot \
 	&& mkdir -p /opt/telegram-bot-api \