Fix minor rst issue
Fix minor rst issue

wbinventor/openmc,walshjon/openmc,paulromano/openmc,walshjon/openmc,amandalund/openmc,wbinventor/openmc,smharper/openmc,kellyrowland/openmc,samuelshaner/openmc,shikhar413/openmc,smharper/openmc,amandalund/openmc,walshjon/openmc,bhermanmit/openmc,liangjg/openmc,shikhar413/openmc,shikhar413/openmc,mit-crpg/openmc,smharper/openmc,liangjg/openmc,johnnyliu27/openmc,wbinventor/openmc,johnnyliu27/openmc,johnnyliu27/openmc,liangjg/openmc,mit-crpg/openmc,liangjg/openmc,wbinventor/openmc,bhermanmit/openmc,mjlong/openmc,kellyrowland/openmc,mit-crpg/openmc,samuelshaner/openmc,paulromano/openmc,paulromano/openmc,amandalund/openmc,mjlong/openmc,walshjon/openmc,mit-crpg/openmc,johnnyliu27/openmc,samuelshaner/openmc,smharper/openmc,samuelshaner/openmc,paulromano/openmc,amandalund/openmc,shikhar413/openmc