developper => developer (#1356)
developper => developer (#1356)

Automatic merge from submit-queue

developper => developer

Typo fix.
```release-note
NONE
```
istio/old_mixer_repo,istio/old_mixer_repo,rkpagadala/mixer,istio/old_mixer_repo,rkpagadala/mixer,rkpagadala/mixer