You should never use nil? in a postfix expr

`nil` values always evaluate `false` and anything else (except, of 
course, `false`) evaulates `true`. So, you can write your postfix
expressions a lot nicer. In the code above, you can read it like...
* print the teamcity build number if it exists
* print the "manual" build number if the teamcity build number does 
  not exist