fix typo (#818)
fix typo (#818)


du2016/prometheus-docs,chosenken/docs,du2016/prometheus-docs,prometheus/docs,ddfreyne/prometheus-docs,chosenken/docs,ddfreyne/prometheus-docs,ddfreyne/prometheus-docs,prometheus/docs,ddfreyne/prometheus-docs,prometheus/docs,chosenken/docs,du2016/prometheus-docs,chosenken/docs