Fixed bug with use of position array. Closes #100 on github.
Fixed bug with use of position array. Closes #100 on github.

kellyrowland/openmc,liangjg/openmc,sxds/opemmc,walshjon/openmc,mjlong/openmc,shikhar413/openmc,liangjg/openmc,walshjon/openmc,samuelshaner/openmc,smharper/openmc,walshjon/openmc,liangjg/openmc,mit-crpg/openmc,samuelshaner/openmc,kellyrowland/openmc,lilulu/openmc,samuelshaner/openmc,shenqicang/openmc,wbinventor/openmc,paulromano/openmc,lilulu/openmc,bhermanmit/openmc,wbinventor/openmc,keadyk/openmc_mg_prepush,sxds/opemmc,paulromano/openmc,mjlong/openmc,amandalund/openmc,lilulu/openmc,mit-crpg/openmc,walshjon/openmc,bhermanmit/cdash,samuelshaner/openmc,shikhar413/openmc,johnnyliu27/openmc,amandalund/openmc,mit-crpg/openmc,shikhar413/openmc,amandalund/openmc,wbinventor/openmc,nhorelik/openmc,smharper/openmc,johnnyliu27/openmc,nhorelik/openmc,paulromano/openmc,shenqicang/openmc,johnnyliu27/openmc,smharper/openmc,shikhar413/openmc,johnnyliu27/openmc,keadyk/openmc_mg_prepush,paulromano/openmc,keadyk/openmc_mg_prepush,smharper/openmc,liangjg/openmc,wbinventor/openmc,amandalund/openmc,bhermanmit/openmc,mit-crpg/openmc