feat: warn about extraneous copyright years

References #17

src/common.ts

@@ -475,6 +475,9 @@ export function checkCopyrightYears(path: PathLike, subDir: PathLike): void {
 
           if (idx >= 0) {
             changedYears.splice(idx, 1);
+          } else {
+            // tslint:disable-next-line:max-line-length
+            consoleWarn(`File '${join(subDir.toString(), fileSystemObject)}' wrongly states '${copyrightYear}' as year in the copyright line.`);
           }
         }