fix context sentences in YAML to ensure vocab emphasis

docs/howtostudykorean/unit-1/19-comparatives.md

@@ -340,9 +340,9 @@ vocabulary:
       audio: https://www.howtostudykorean.com/wp-content/uploads/2015/11/Lesson19v29.mp3
       en: less
       examples:
-        - ko: 나는 남동생보다 덜 잘생겼어
+        - ko: 나는 남동생보다 **덜** 잘생겼어
           audio: https://www.howtostudykorean.com/wp-content/uploads/2017/03/Lesson19-30.mp3
-          en: I'm less handsome than my brother
+          en: I'm **less** handsome than my brother
         - ko: 한국에서 대학교는 고등학교보다 **덜** 어려워요
           audio: https://www.howtostudykorean.com/wp-content/uploads/2017/03/Lesson19-31.mp3
           en: In Korea, University is **not as hard** as high school