fix(styleguide): improve font rendering for h3 styles on IE9 and IE10
fix(styleguide): improve font rendering for h3 styles on IE9 and IE10

[Finishes #82065438]

Signed-off-by: Bebe Peng <cc70e5ee229c0d4b3ccc63a88c70622c84c389ff@pivotal.io>

sjolicoeur/pivotal-ui,pivotal-cf/pivotal-ui,npm/pivotal-ui,sjolicoeur/pivotal-ui,CanopyCloud/pivotal-ui,npm/pivotal-ui,CanopyCloud/pivotal-ui,pivotal-cf/pivotal-ui,sjolicoeur/pivotal-ui,pivotal-cf/pivotal-ui,CanopyCloud/pivotal-ui,npm/pivotal-ui,sjolicoeur/pivotal-ui