adding global variable animation-speed (#477)

Fixes #476

Author: kylebuch8

elements/pfe-sass/variables/_maps.scss

@@ -219,6 +219,7 @@ $pfe-vars: (
   box-shadow--lg:                '0  #{pfe-size-prem(3)}  #{pfe-size-prem(7)} #{pfe-size-prem(3)} rgba(#{$pfe-color--gray-1000}, .13), 0  #{pfe-size-prem(11)}  #{pfe-size-prem(24)} #{pfe-size-prem(16)} rgba(#{$pfe-color--gray-1000}, .12)',
   box-shadow--inset:             'inset 0 0 #{pfe-size-prem(10)} 0 rgba(#{$pfe-color--gray-1000}, .25)',
 
+  animation-speed:               0.3,
   animation-timing:              cubic-bezier(0.465, 0.183, 0.153, 0.946),
   opacity:                       .3
 );