inky: run stringer with "go run" (#95)

Run stringer command (for code generation) using "go run" instead of "go
install" to avoid affecting the developer's global $GOBIN.

inky/types.go

@@ -4,7 +4,7 @@
 
 package inky
 
-//go:generate go install golang.org/x/tools/cmd/stringer@latest
+//go:generate -command stringer go run golang.org/x/tools/cmd/stringer@latest
 //go:generate stringer -type=Model,Color,ImpressionColor -output types_string.go
 
 import (