fixed typos in mgxs
fixed typos in mgxs

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