Update dependency which to v1.3.1 (#347)

Author: renovate[bot]

package-lock.json

@@ -51,7 +51,7 @@
     "selenium-assistant": "5.3.0",
     "semver": "5.5.0",
     "sinon": "6.0.0",
-    "which": "1.3.0"
+    "which": "1.3.1"
   },
   "engines": {
     "node": ">= 4"