fix: slight grammar fix in warning message

Note: The following breaking change was implemented and documented in
3e6355b, before `semantic-release` was brought in.

BREAKING CHANGE:

The `executablePath` setting has been removed and is no longer
available. `linter-pug` will now use your project's local `pug-lint`
when one can be found using the standard `require.resolve`
implementation. If one can't be found local to your project then the
bundled one will be used as a fallback.

lib/init.js

@@ -74,7 +74,7 @@ module.exports = {
         {
           detail: 'linter-pug has moved to the Node.js API for pug-lint and ' +
             "will now use a project's local instance where possible, falling " +
-            'back to a bundled version of pug-lint where none is found.',
+            'back to a bundled version of pug-lint if none is found.',
         },
       );
       atom.config.unset('linter-pug.executablePath');