Make sure that we always fetch latest commit sha

When we update the service definition we don't want to copy sha from
the previous deployment but rather fetch the latest one. For that
we need to zero git sha in deployment definiton which will trigger
fetching latest change.

pkg/koyeb/services.go

@@ -165,6 +165,11 @@ $> koyeb service update myapp/myservice --env PORT=8001 --env '!DEBUG'`,
 				updateDef = latestDeploy.GetDeployments()[0].Definition
 			}
 
+			// zero the sha to make sure that the latest sha is fetched
+			if updateDef.Git != nil {
+				updateDef.Git.Sha = koyeb.PtrString("")
+			}
+
 			err = parseServiceDefinitionFlags(cmd.Flags(), updateDef)
 			if err != nil {
 				return err