Fix a race condition

Make it so if the editor contents have changed between when the lint was
triggered and the results came back we simply tell Linter to not update
the current messages, instead of attempting to mark up the contents based
on the old (potentially leading to "invalid" ranges, that _were_ valid when
the lint was triggered).

Author: Arcanemagus

lib/index.js

@@ -61,6 +61,11 @@ export function provideLinter() {
 
       const messages = HTMLHint.verify(fileText, ruleset || undefined);
 
+      if (editor.getText() !== fileText) {
+        // Editor contents have changed, tell Linter not to update
+        return null;
+      }
+
       return messages.map(message => ({
         range: rangeFromLineNumber(editor, message.line - 1, message.col - 1),
         type: message.type,