chore(radio): change from $neutral-5 to $gray-5
chore(radio): change from $neutral-5 to $gray-5

these are the same color, just using a different variable

[#113502223]

Signed-off-by: Elena Sharma <b378d1ba98e37e93964405ef527305746a4ce2c5@pivotal.io>

pivotal-cf/pivotal-ui,sjolicoeur/pivotal-ui,pivotal-cf/pivotal-ui,sjolicoeur/pivotal-ui,sjolicoeur/pivotal-ui,pivotal-cf/pivotal-ui,sjolicoeur/pivotal-ui