Add no-alt-text rule to accessibility.json (#18)

* Add no-alt-text rule

* Update test

Author: khiga8

style/accessibility.json

@@ -1,4 +1,5 @@
 {
+    "no-alt-text": true,
     "no-default-alt-text": true,
     "no-duplicate-header": true,
     "no-emphasis-as-header": true,

test/usage.test.js

@@ -25,6 +25,7 @@ describe("usage", () => {
         "no-blanks-blockquote": false,
         "fenced-code-language": true,
         "no-default-alt-text": true,
+        "no-alt-text": true,
       });
     });