fix context sentences in YAML to ensure vocab emphasis

docs/howtostudykorean/unit-1/20-well-poorly.md

@@ -188,9 +188,9 @@ vocabulary:
         못하다 has the opposite meaning of 잘하다. For example:
         - "나는 수영을 못해" = "I am bad at swimming"
       examples:
-        - ko: 나는 수영을 못해
+        - ko: 나는 수영을 **못해**
           en: I am **bad at** swimming
-        - ko: 저 학생은 공부를 못해
+        - ko: 저 학생은 공부를 **못해**
           audio: https://www.howtostudykorean.com/wp-content/uploads/2017/03/Lesson20-10.mp3
           en: That student does **not** study **well**
         - ko: 제가 너무 부끄러워서 발표를 **못해요**
@@ -406,9 +406,9 @@ vocabulary:
 
         The usage of 못 is very complex. See below in this lesson for more information.
       examples:
-        - ko: 저는 어제 시험을 못 봤어요
+        - ko: 저는 어제 시험을 **못** 봤어요
           audio: https://www.howtostudykorean.com/wp-content/uploads/2017/03/Lesson20-12.mp3
-          en: I did **poorly** on the exam yesterday / I didn't write the exam yesterday
+          en: I did **poorly** on the exam yesterday / I **didn't** write the exam yesterday
         - ko: 이 셔츠가 너무 작아서 **못** 입어요
           en: I **can't** put this shirt on because it is too small
         - ko: 저는 그 동안 공부를 **못** 했어요