Fix proselint timeout by copying 60 seconds hard limit and uniqueKey from linter-bootlint …

[sladewin]

…and added null check for results

This is a fix for linter-proselint timeouts that occur linting large files with thousands or ten of thousands of lines, originally identified in #4
Copied a fix from linter-bootlint that added a 60 seconds hard limit to the linting process. Error identified here: AtomLinter/linter-bootlint#44

Also, identified a problem caused by sequential linting requests being invoked before the preceding linting has completed causing the linter to return a null. Caused by CTRL+S saving forced a re-lint before the previous request is finished. Fix is to ignore subsequent lint requests and dummy in a non-null return value.

@Arcanemagus

[gammacray]

Thanks for this. I was having the same problem with timeouts and I injected your code, proselint runs like a top. This was officially my first time messing with, so I feel pretty accomplished! : )

Cheers.