Update ava to the latest version 🚀 (#450)

* chore(package): update ava to version 0.19.0

https://greenkeeper.io/

* Fix tests for latest ava

test/expressions.js

@@ -0,0 +1,5 @@
+import path from "path";
+import { runFixtureTests } from "./helpers/runFixtureTests";
+import { parseExpression } from "../lib";
+
+runFixtureTests(path.join(__dirname, "expressions"), parseExpression);