Use env lib, add PROXY_PORT ENV variable

vendor/github.com/caarlos0/env/parsers/parsers.go

@@ -0,0 +1,23 @@
+// Package parsers contains custom parser funcs for common, non-built-in types
+package parsers
+
+import (
+	"fmt"
+	"net/url"
+	"reflect"
+)
+
+var (
+	// URLType is a helper var that represents the `reflect.Type`` of `url.URL`
+	URLType = reflect.TypeOf(url.URL{})
+)
+
+// URLFunc is a basic parser for the url.URL type that should be used with `env.ParseWithFuncs()`
+func URLFunc(v string) (interface{}, error) {
+	u, err := url.Parse(v)
+	if err != nil {
+		return nil, fmt.Errorf("Unable to complete URL parse: %v", err)
+	}
+
+	return *u, nil
+}