chore(env): OPENVPN_CIPHERS variable

- With retro-compatibility with `OPENVPN_CIPHER`

Dockerfile

@@ -81,7 +81,7 @@ ENV VPN_SERVICE_PROVIDER=pia \
     OPENVPN_VERSION=2.5 \
     OPENVPN_VERBOSITY=1 \
     OPENVPN_FLAGS= \
-    OPENVPN_CIPHER= \
+    OPENVPN_CIPHERS= \
     OPENVPN_AUTH= \
     OPENVPN_PROCESS_USER= \
     OPENVPN_IPV6=off \

internal/configuration/sources/env/openvpn.go

@@ -23,7 +23,9 @@ func (r *Reader) readOpenVPN() (
 		openVPN.ConfFile = &confFile
 	}
 
-	openVPN.Ciphers = envToCSV("OPENVPN_CIPHER")
+	_, ciphersCSV := r.getEnvWithRetro("OPENVPN_CIPHERS", "OPENVPN_CIPHER")
+	openVPN.Ciphers = strings.Split(ciphersCSV, ",")
+
 	auth := os.Getenv("OPENVPN_AUTH")
 	if auth != "" {
 		openVPN.Auth = &auth