Fix guards creation

```
git clone https://github.com/gae-init/gae-init.git
cd gae-init
./run.py -s
Traceback (most recent call last):
  File "./run.py", line 635, in <module>
    run()
  File "./run.py", line 613, in run
    install_dependencies()
  File "./run.py", line 375, in install_dependencies
    with open(FILE_NPM_GUARD, 'w') as npm_guard:
IOError: [Errno 2] No such file or directory: 'temp/npm.guard'
```
Oops...