feat(cli): add command for upgrading one plugin

pkg/cmd/grafana-cli/commands/upgrade_command.go

@@ -1,9 +1,33 @@
 package commands
 
 import (
-	"errors"
+	s "github.com/grafana/grafana/pkg/cmd/grafana-cli/services"
 )
 
 func upgradeCommand(c CommandLine) error {
-	return errors.New("Not yet Implemented")
+	pluginDir := c.GlobalString("path")
+	pluginName := c.Args().First()
+
+	localPlugin, err := s.ReadPlugin(pluginDir, pluginName)
+
+	if err != nil {
+		return err
+	}
+
+	remotePlugins, err2 := s.ListAllPlugins()
+
+	if err2 != nil {
+		return err2
+	}
+
+	for _, v := range remotePlugins.Plugins {
+		if localPlugin.Id == v.Id {
+			if ShouldUpgrade(localPlugin.Info.Version, v) {
+				s.RemoveInstalledPlugin(pluginDir, pluginName)
+				return InstallPlugin(localPlugin.Id, pluginDir, "")
+			}
+		}
+	}
+
+	return nil
 }