[ML] Say 'rarer' instead of 'more rare'.

x-pack/plugins/ml/public/explorer/explorer_charts/explorer_chart_info_tooltip.js

@@ -14,7 +14,7 @@ import { CHART_TYPE } from '../explorer_constants';
 
 const CHART_DESCRIPTION = {
   [CHART_TYPE.EVENT_DISTRIBUTION]: 'The gray dots depict the distribution of occurences over time for a sample of by_field_values with \
-more frequent event types at the top and more rare ones at the bottom.',
+more frequent event types at the top and rarer ones at the bottom.',
   [CHART_TYPE.POPULATION_DISTRIBUTION]: 'The gray dots depict the distribution of values over time for a sample of over_field_values.'
 };