Update index.js

Author: nicolaskruchten

src/traces/indicator/index.js

@@ -24,7 +24,7 @@ module.exports = {
 
     meta: {
         description: [
-            'An indicator is used to visualize single a `value` along with some',
+            'An indicator is used to visualize a single `value` along with some',
             'contextual information such as `steps` or a `threshold`, using a',
             'combination of three visual elements: a number, a delta, and/or a gauge.',
             'Deltas are taken with respect to a `reference`.',