refactor: revise obsolete kata logic (#855)

Method name has changed from `second_symbol` to `secondSymbol`.

Author: ParanoidUser

kata/7-kyu/find-the-index-of-the-second-occurrence-of-a-letter-in-a-string/main/SecondOcurrence.java

@@ -1,5 +1,5 @@
 interface SecondOcurrence {
-  static int second_symbol(String str, char c) {
+  static int secondSymbol(String str, char c) {
     return str.indexOf(c, str.indexOf(c) + 1);
   }
 }

kata/7-kyu/find-the-index-of-the-second-occurrence-of-a-letter-in-a-string/test/SolutionTest.java

@@ -5,10 +5,10 @@
 class SolutionTest {
   @Test
   void sample() {
-    assertEquals(3, SecondOcurrence.second_symbol("Hello world!!!", 'l'));
-    assertEquals(7, SecondOcurrence.second_symbol("Hello world!!!", 'o'));
-    assertEquals(-1, SecondOcurrence.second_symbol("Hello world!!!", 'A'));
-    assertEquals(-1, SecondOcurrence.second_symbol("Hello", '!'));
-    assertEquals(-1, SecondOcurrence.second_symbol("", 'q'));
+    assertEquals(3, SecondOcurrence.secondSymbol("Hello world!!!", 'l'));
+    assertEquals(7, SecondOcurrence.secondSymbol("Hello world!!!", 'o'));
+    assertEquals(-1, SecondOcurrence.secondSymbol("Hello world!!!", 'A'));
+    assertEquals(-1, SecondOcurrence.secondSymbol("Hello", '!'));
+    assertEquals(-1, SecondOcurrence.secondSymbol("", 'q'));
   }
 }