Convert nine

tcr-roman-numerals/src/main/java/fr/ippon/kata/numeral/Numerals.java

@@ -22,6 +22,7 @@ public class Numerals {
     conversions.put(1, "I");
     conversions.put(4, "IV");
     conversions.put(5, "V");
+    conversions.put(9, "IX");
 
     return conversions;
   }

tcr-roman-numerals/src/test/java/fr/ippon/kata/numeral/NumeralsTest.java

@@ -35,4 +35,9 @@ class NumeralsTest {
   void shouldConvertSixToVI() {
     assertThat(Numerals.toRoman(6)).isEqualTo("VI");
   }
+
+  @Test
+  void shouldConvertNineToIX() {
+    assertThat(Numerals.toRoman(9)).isEqualTo("IX");
+  }
 }