dnanexus build failure

[dpark01]

The actual compiling and publishing of WDLs to dnanexus works fine but the building of the launcher workflows appears to be failing here:

~/work/viral-pipelines/viral-pipelines/pipes/dnax/dx-launcher ~/work/viral-pipelines/viral-pipelines
Traceback (most recent call last):
  File "./dx-yml-build", line 17, in <module>
    data = yaml.load(infile)
TypeError: load() missing 1 required positional argument: 'Loader'
Error: Process completed with exit code 1.

This does not affect branch builds at the moment (which are skipping the dnax builds) but only the master branch builds

[dpark01]

This was fixed in #488