Use template literal instead of concating number and string (#4593)
Use template literal instead of concating number and string (#4593)

Fixes https://github.com/kythe/kythe/pull/4591#discussion_r456686833
kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe,kythe/kythe