node-gyp@4.x is not released yet

appveyor.yml

@@ -24,7 +24,7 @@ install:
   # upgrade node-gyp to dodge https://github.com/mapbox/node-pre-gyp/issues/209#issuecomment-307641388
   # and allow make node 4.x x86 builds work
   # https://github.com/mapbox/node-pre-gyp/issues/209#issuecomment-217690537
-  - IF "%nodejs_version:~0,1%"=="4" npm install node-gyp@4.x
+  - IF "%nodejs_version:~0,1%"=="4" npm install node-gyp@3.x
   # downgrade npm to avoid multiple npm bugs:
   # for node v6 this dodges npm 3.10.10 bug whereby --nodedir/--dist-url is not passed to node-gyp (https://github.com/mapbox/node-pre-gyp/issues/300)
   # for all node x86 versions this dodges a mysterious ELIFECYCLE error: https://ci.appveyor.com/project/Mapbox/node-pre-gyp/build/1.0.582/job/b8q2nud6vkj0s6qo#L233