docs: update descriptions

Author: kgryte

lib/node_modules/@stdlib/array/index/lib/main.js

@@ -252,7 +252,7 @@ setReadOnly( ArrayIndex, 'get', function get( id ) {
 });
 
 /**
-* Returns the underlying array data of array index object.
+* Returns the underlying array data of an array index object.
 *
 * @name data
 * @memberof ArrayIndex.prototype
@@ -277,7 +277,7 @@ setReadOnlyAccessor( ArrayIndex.prototype, 'data', function get() {
 });
 
 /**
-* Returns the underlying array data type of array index object.
+* Returns the underlying array data type of an array index object.
 *
 * @name dtype
 * @memberof ArrayIndex.prototype
@@ -348,7 +348,7 @@ setReadOnlyAccessor( ArrayIndex.prototype, 'isCached', function get() {
 });
 
 /**
-* Returns the type of array index object.
+* Returns the type of an array index object.
 *
 * @name type
 * @memberof ArrayIndex.prototype