pull request browser open failed on chromium

This is very minor but the nice browser opening failed on my machine. See below.  

```
<== Pull request opened at: 'https://github.com/ros/rosdistro/pull/1079'
sh: 0: getcwd() failed: No such file or directory
tfoote@BigFoote:/data/tmp/filters_test/src/filters$ [26032:26032:0626/181404:ERROR:process_singleton_linux.cc(263)] Failed to create /home/tfoote/.config/chromium/SingletonLock: File exists
[26032:26032:0626/181404:ERROR:chrome_browser_main.cc(1066)] Failed to create a ProcessSingleton for your profile directory. This means that running multiple instances would start multiple browser processes rather than opening a new window in the existing process. Aborting now to avoid profile corruption.
```