apk add: pinned versions (hadolint/DL3018)

https://github.com/hadolint/hadolint/wiki/DL3018
https://docs.docker.com/engine/articles/dockerfile_best-practices/

CHANGELOG.md

@@ -7,6 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 ### Added
 - Changelog
+- apk add: pinned versions of tor & obfs4proxy
 
 ### Fixed
 - ansible-playbook: fixed invalid keyword

Dockerfile

@@ -2,8 +2,8 @@
 FROM alpine:3.10
 
 RUN adduser -S onion \
-    && apk add --no-cache tor \
-    && apk add --no-cache obfs4proxy \
+    && apk add --no-cache tor=~0.3.5.8 \
+    && apk add --no-cache obfs4proxy=~0.0.7 \
         --repository http://dl-cdn.alpinelinux.org/alpine/edge/testing
 
 ENV OR_PORT=