Workaround travis hangs by using default SDK version of pub (#2224)

* Reduce the amount of precompiling to fix hangs when building flutter docs.

* Add verbose flag to figure out what's really going on

* Stop using flutter pub

Author: jcollins-g

tool/grind.dart

@@ -770,8 +770,10 @@ Future<List<Map>> _buildFlutterDocs(
     ['get'],
     workingDirectory: path.join(flutterPath, 'dev', 'snippets'),
   );
+  // TODO(jcollins-g): flutter's dart SDK pub tries to precompile the universe
+  // when using -spath.  Why?
   await flutterRepo.launcher.runStreamed(
-      flutterRepo.cachePub, ['global', 'activate', '-spath', '.'],
+      'pub', ['global', 'activate', '-spath', '.', '-x', 'dartdoc'],
       workingDirectory: await futureCwd);
   return await flutterRepo.launcher.runStreamed(
     flutterRepo.cacheDart,