Set indentation to 4 and only use spaces

Author: ianding1

autoload/leetcode.vim

@@ -1,4 +1,5 @@
-" vim: sts=4 sw=4
+" vim: sts=4 sw=4 expandtab
+
 let s:current_dir = expand("<sfile>:p:h")
 
 python3 <<EOF

plugin/leetcode.vim

@@ -1,3 +1,5 @@
+" vim: sts=4 sw=4 expandtab
+
 if !exists('g:leetcode_username')
     let g:leetcode_username = ''
 endif