Merge pull request #281 from zeromq/greenkeeper/prebuild-8.1.0

chore(package): update prebuild to version 8.1.0

Author: lgeiger

package.json

@@ -17,7 +17,7 @@
     "jsdoc": "^3.5.4",
     "mocha": "^5.0.0",
     "nyc": "^12.0.2",
-    "prebuild": "^7.6.0",
+    "prebuild": "^8.1.0",
     "semver": "^5.4.1",
     "should": "^13.0.0"
   },