node-gyp failure with npm 5.8.0

Nobody has claimed this yet.

node-pre-gyp fails in the node-gyp step with the following error (example using the vtquery module):

```
Error: Failed to execute 'node-gyp configure ...
```

Stack trace
```
V=1 ./node_modules/.bin/node-pre-gyp configure build --error_on_warnings=true --loglevel=error
NPM BASE /Users/mapsam/.nvm/versions/node/v6.13.0/lib/node_modules/npm/
NPM GYP BIN /Users/mapsam/.nvm/versions/node/v6.13.0/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js
node-pre-gyp ERR! configure error
node-pre-gyp ERR! stack Error: Failed to execute 'node-gyp configure --error_on_warnings=true --loglevel=error --module=/Users/mapsam/mapbox/vtquery/lib/binding/vtquery.node --module_name=vtquery --module_path=/Users/mapsam/mapbox/vtquery/lib/binding' (Error: spawn node-gyp ENOENT)
node-pre-gyp ERR! stack at ChildProcess. (/Users/mapsam/mapbox/vtquery/node_modules/node-pre-gyp/lib/util/compile.js:80:29)
node-pre-gyp ERR! stack at emitOne (events.js:96:13)
node-pre-gyp ERR! stack at ChildProcess.emit (events.js:188:7)
node-pre-gyp ERR! stack at Process.ChildProcess._handle.onexit (internal/child_process.js:217:12)
node-pre-gyp ERR! stack at onErrorNT (internal/child_process.js:376:16)
node-pre-gyp ERR! stack at _combinedTickCallback (internal/process/next_tick.js:80:11)
node-pre-gyp ERR! stack at process._tickCallback (internal/process/next_tick.js:104:9)
node-pre-gyp ERR! stack at Module.runMain (module.js:613:11)
node-pre-gyp ERR! stack at run (bootstrap_node.js:387:7)
node-pre-gyp ERR! stack at startup (bootstrap_node.js:153:9)
node-pre-gyp ERR! System Darwin 17.4.0
node-pre-gyp ERR! command "/Users/mapsam/.nvm/versions/node/v6.13.0/bin/node" "/Users/mapsam/mapbox/vtquery/node_modules/.bin/node-pre-gyp" "configure" "build" "--error_on_warnings=true" "--loglevel=error"
node-pre-gyp ERR! cwd /Users/mapsam/mapbox/vtquery
node-pre-gyp ERR! node -v v6.13.0
node-pre-gyp ERR! node-pre-gyp -v v0.6.39
node-pre-gyp ERR! not ok
Failed to execute 'node-gyp configure --error_on_warnings=true --loglevel=error --module=/Users/mapsam/mapbox/vtquery/lib/binding/vtquery.node --module_name=vtquery --module_path=/Users/mapsam/mapbox/vtquery/lib/binding' (Error: spawn node-gyp ENOENT)
```

* node version: v6.13.0
* npm version: 5.8.0

It appears this is an issue with the most recent npm release, version 5.8.0, which was released on 03/08/2018 and removed the node-gyp module unexpectedly. https://github.com/npm/npm/issues/20163. The following path is [created in node-pre-gyp](https://github.com/mapbox/node-pre-gyp/blob/cf559670e6a59768437bd35229cdd06988e4748e/lib/util/compile.js#L48-L51) with the assumption that node-gyp exists in npm.

```
/Users/mapsam/.nvm/versions/node/v6.13.0/lib/node_modules/npm/node_modules/node-gyp/bin/
```

We'll continue to monitor over there to learn whether we need a fix here or if we can just update to a future version.

cc @springmeyer @millzpaugh

Start with lib/util/compile.js at the linked lines and compare its node-gyp path assumption with the npm issue linked in the report. Reproduce the failure with Node v6.13.0 and npm 5.8.0, then determine whether node-pre-gyp needs a fix or whether an upstream npm release resolves it.

Written by the indexing model from the issue text.