Ignore existing heading anchor

[lamyergeier]

Current Output:

echo "# List of Tasks {#list-of-task}" | markdown-toc -
- [List of Tasks {#list-of-task}](#list-of-tasks-%23list-of-task)

Desired Output:

echo "# List of Tasks {#list-of-task}" | markdown-toc -
- [List of Tasks](#list-of-tasks)