vimrc(airline): enable mixed-indent algo warning

.vim/vimrc

@@ -118,9 +118,14 @@ let g:airline_mode_map = {
       \ 'V'      : 'V-L',
       \ ''     : 'V-B',
       \ }
+
 " skip displaying fileformat output if the output matches a configured string.
 let g:airline#parts#ffenc#skip_expected_string='utf-8[unix]'
 
+" certain number of spaces are allowed after tabs, but not in between.
+" this algorithm works well for /** */ style comments in a tab-indented file.
+let g:airline#extensions#whitespace#mixed_indent_algo = 1
+
 " ale integration
 let g:airline#extensions#ale#enabled = 1
 " nrrwrgn integration