Upgrade Alpine version to 3.9, add ca-certificates

Author: erickskrauch

CHANGELOG.md

@@ -32,6 +32,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 - Bumped Go version to 1.12.
+- Bumped Alpine version to 3.9.3.
 
 ### Fixed
 - `/textures` request no longer proxies request to Mojang in a case when there is no information about the skin,

Dockerfile

@@ -1,7 +1,9 @@
-FROM alpine:3.7
+FROM alpine:3.9.3
 
 EXPOSE 80
 
+RUN apk add --no-cache ca-certificates
+
 ENV STORAGE_REDIS_HOST=redis
 ENV STORAGE_FILESYSTEM_HOST=/data