At the moment you can never be sure whether you look at the results
that ale just produced after your last changes or you are looking at
outdated information.
Instead of showing the last results while ale executes checks on the
current buffer it can now show a specific indicator.
This commit introduces the new config variable
`g:airline#extensions#ale#checking_symbol` which defaults to "...". In
case you don't want to see this, you may set it to an empty string.
0609a1f945