feat(docker): upgrade Alpine to 3.15

Dockerfile

@@ -1,5 +1,5 @@
-ARG ALPINE_VERSION=3.14
-ARG GO_ALPINE_VERSION=3.14
+ARG ALPINE_VERSION=3.15
+ARG GO_ALPINE_VERSION=3.15
 ARG GO_VERSION=1.17
 ARG XCPUTRANSLATE_VERSION=v0.6.0
 ARG GOLANGCI_LINT_VERSION=v1.43.0

README.md

@@ -61,7 +61,7 @@ using Go, OpenVPN or Wireguard, iptables, DNS over TLS, ShadowSocks and an HTTP
 
 ## Features
 
-- Based on Alpine 3.14 for a small Docker image of 33MB
+- Based on Alpine 3.15 for a small Docker image of 29MB
 - Supports: **Cyberghost**, **ExpressVPN**, **FastestVPN**, **HideMyAss**, **IPVanish**, **IVPN**, **Mullvad**, **NordVPN**, **Perfect Privacy**, **Privado**, **Private Internet Access**, **PrivateVPN**, **ProtonVPN**, **PureVPN**,  **Surfshark**, **TorGuard**, **VPNUnlimited**, **Vyprvpn**, **WeVPN**, **Windscribe** servers
 - Supports OpenVPN for all providers listed
 - Supports Wireguard both kernelspace and userspace