Update dependency ava to v3.15.0

Author: renovate-bot

package.json

@@ -40,7 +40,7 @@
     "@babel/polyfill": "7.8.7",
     "@babel/preset-env": "7.9.5",
     "@babel/register": "7.9.0",
-    "ava": "^3.7.1",
+    "ava": "3.15.0",
     "coveralls": "^3.0.14",
     "esdoc": "^1.1.0",
     "esdoc-inject-script-plugin": "1.0.0",