Using whatever "true" is available.  fixes #82

since `/usr/bin/true` appears to be an OSX/BSD thing whereas the build
workers are (mostly? all?) Linux, which has `/bin/true`, plus the fact
that `true` is a bash builtin...
Merge pull request #85 from meatballhat/fix-true-for-go-builds-82

Using whatever "true" is available.  fixes #82