commitlint/plugins: fix the rule

If the subject contains just the word "fix", and there's no
commit msg body, this rule should complain.

Author: tehraninasab

commitlint/plugins.ts

@@ -281,6 +281,8 @@ export abstract class Plugins {
 
             if (firstWordInTitle === "update") {
                 offence = titleWords.length > 1 && bodyStr === null;
+            } else if (firstWordInTitle === "fix") {
+                offence = bodyStr === null;
             } else {
                 offence = obviousWords.includes(firstWordInTitle);
             }