Update to latest prebuildify + use ~ ranges for dependencies (#571)

Author: Lars-Magnus Skog

package.json

@@ -16,8 +16,8 @@
     "abstract-leveldown": "~6.0.0",
     "bindings": "~1.3.0",
     "fast-future": "~1.0.2",
-    "napi-macros": "^1.8.1",
-    "node-gyp-build": "^3.5.1"
+    "napi-macros": "~1.8.1",
+    "node-gyp-build": "~3.7.0"
   },
   "devDependencies": {
     "async": "^2.0.1",
@@ -31,7 +31,7 @@
     "node-gyp": "^3.8.0",
     "nyc": "^12.0.2",
     "optimist": "~0.6.1",
-    "prebuildify": "ralphtheninja/prebuildify",
+    "prebuildify": "^2.10.0",
     "prebuildify-ci": "^1.0.4",
     "readfiletree": "~0.0.1",
     "rimraf": "^2.6.1",