Fix the config key for old setting migration

It looks like the config key that was set for old settings migrations
was unfortunately set to `linter-pylint.executablePath` instead of the
equivalent `linter-clang` key.

Author: Arcanemagus

lib/main.js

@@ -88,7 +88,7 @@ export default {
       atom.config.unset('linter-clang.execPath');
       if (oldPath !== 'clang') {
         // If the old config wasn't set to the default migrate it over
-        atom.config.set('linter-pylint.executablePath', oldPath);
+        atom.config.set('linter-clang.executablePath', oldPath);
       }
     }