Fix suspicious method call. #1555

Fixes SuspiciousMethodCalls inspection violation.

Description:
>This inspection reports method calls to parameterized collections, where actual argument type does not correspond to the collection's elements type.  For example if you have the following code:
 ```
     List<Integer> list = getListOfElements();
     list.remove("");
 ```
 the call to `remove()` will be highlighted.

src/main/java/com/puppycrawl/tools/checkstyle/checks/indentation/LineSet.java

@@ -51,7 +51,7 @@ public class LineSet {
      * @return the starting column for the first line.
      */
     public int firstLineCol() {
-        final Object firstLineKey = lines.firstKey();
+        final Integer firstLineKey = lines.firstKey();
         return lines.get(firstLineKey);
     }