Shim bare numbers into duration strings [#39]

Helm2's --timeout took a number of seconds, rather than the
ParseDuration-compatible string that helm3 uses. For backward-
compatibility, update a bare number into a duration string.

internal/helm/config.go

@@ -4,8 +4,11 @@ import (
 	"fmt"
 	"github.com/kelseyhightower/envconfig"
 	"io"
+	"regexp"
 )
 
+var justNumbers = regexp.MustCompile(`^\d+$`)
+
 // The Config struct captures the `settings` and `environment` blocks in the application's drone
 // config. Configuration in drone's `settings` block arrives as uppercase env vars matching the
 // config key, prefixed with `PLUGIN_`. Config from the `environment` block is uppercased, but does
@@ -62,6 +65,10 @@ func NewConfig(stdout, stderr io.Writer) (*Config, error) {
 		}
 	}
 
+	if justNumbers.MatchString(cfg.Timeout) {
+		cfg.Timeout = fmt.Sprintf("%ss", cfg.Timeout)
+	}
+
 	if cfg.Debug && cfg.Stderr != nil {
 		cfg.logDebug()
 	}