chore(deps): update dependency @sourcegraph/eslint-config to ^0.20.15

Author: renovate-bot

package.json

@@ -117,7 +117,7 @@
   "devDependencies": {
     "@commitlint/cli": "^11.0.0",
     "@commitlint/config-conventional": "^11.0.0",
-    "@sourcegraph/eslint-config": "^0.20.8",
+    "@sourcegraph/eslint-config": "^0.20.15",
     "@sourcegraph/prettierrc": "^3.0.3",
     "@sourcegraph/tsconfig": "^3.0.0",
     "@types/mocha": "7.0.2",