chore(package): update ava to version 0.20.0

Author: greenkeeper[bot]

package.json

@@ -29,7 +29,7 @@
     "@aureooms/js-compare": "^1.4.5",
     "@aureooms/js-itertools": "^3.1.1",
     "@aureooms/js-random": "^2.0.0",
-    "ava": "^0.19.1",
+    "ava": "^0.20.0",
     "babel-cli": "^6.22.2",
     "babel-polyfill": "^6.22.0",
     "babel-preset-latest": "^6.22.0",