better callingNumberKorean impl

packages/utils/callingNumberKorean.ts

@@ -8,10 +8,6 @@ export default class CallingNumberKorean {
         "", "한", "두", "세", "네", "다섯",
         "여섯", "일곱", "여덟", "아홉", "열",
     ]
-    static FirstDigitSingle = [
-        "영", "한", "두", "세", "네", "다섯",
-        "여섯", "일곱", "여덟", "아홉", "열",
-    ]
     static canConvert(num: number): boolean {
         return num < 100 && num >= 0 && Number.isInteger(num)
     }
@@ -19,13 +15,15 @@ export default class CallingNumberKorean {
         const firstDigit = num % 10;
         const secondDigit = Math.floor(num / 10);
 
-        if (secondDigit) {
-            return (
+        let result = (
             this.SecondDigit[secondDigit]
             + this.FirstDigit[firstDigit]
         );
-        } else {
-            return this.FirstDigitSingle[firstDigit];
+
+        if (!result.length) {
+            result = "영"
         }
+
+        return result;
     }
 }