graphviz error on ndtv windows build

[skyebend]

this error showed up in statnet's windows nightly build

* checking tests ... ERROR
Running the tests in 'tests/layout_tests.R' failed.
Last 13 lines of output:
   -m[v]       - Memory test - v iterations.

   -c          - Configure plugins (Writes $prefix/lib/graphviz/config 
                 with available plugin information.  Needs write privilege.)
   -?          - Print usage and exit
  character(0)
  attr(,"status")
  [1] 1
  Error: error$message does not match "Error".
  Actual value: "Unable to parse coordinates returned from Graphviz"
  In addition: Warning message:
  running command 'neato -Tplain -Xhelloworld C:\Users\skyebend\AppData\Local\Temp\Rtmpys7JsZ\network40878ee2048.dot' had status 1 
  Execution halted

[skyebend]

turns out this was only showing up on the windows build because the graphviz tests are set to not run if Graphviz is not installed

[skyebend]

This should be fixed by https://github.com/statnet/ndtv/commit/140b15c0bd47ae7082893bea7d76f0c08b9c82bb