lib: log as yes/no whether build dir was created (#2370)

This bit of logging apparently expected to be given a boolean, but was
receiving either a path or undefined based on the result of fs.mkdir.

Now it prints either "Yes" or "No",
rather than printing either a path or "undefined", respectively.

lib/configure.js

@@ -76,7 +76,9 @@ function configure (gyp, argv, callback) {
       if (err) {
         return callback(err)
       }
-      log.verbose('build dir', '"build" dir needed to be created?', isNew)
+      log.verbose(
+        'build dir', '"build" dir needed to be created?', isNew ? 'Yes' : 'No'
+      )
       if (win) {
         findVisualStudio(release.semver, gyp.opts.msvs_version,
           createConfigFile)