cmd/toolstash: use strings.LastIndexAny

Change-Id: I06a4610a5f5c49806a1b151a65c25bbbd881a314
Reviewed-on: https://go-review.googlesource.com/38753
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/cmd/toolstash/main.go b/cmd/toolstash/main.go
index e1bed36..a77171f 100644
--- a/cmd/toolstash/main.go
+++ b/cmd/toolstash/main.go
@@ -219,10 +219,7 @@
 	}
 
 	tool = cmd[0]
-	if i := strings.LastIndex(tool, "/"); i >= 0 {
-		tool = tool[i+1:]
-	}
-	if i := strings.LastIndex(tool, `\`); i >= 0 {
+	if i := strings.LastIndexAny(tool, `/\`); i >= 0 {
 		tool = tool[i+1:]
 	}