Fix a plugin error on windows 2012 using spaces in the plugin path

this is the simple fix from https://github.com/virgo-agent-toolkit/rackspace-monitoring-agent/pull/549

https://github.com/virgo-agent-toolkit/rackspace-monitoring-agent/pull/549 is stalled while we sort out the build and test system on other oses where gyp does not support spaces in file names.