Use correct function name for degrade breakpoint parsing

@include degrade([breakpoint]) was producing invalid CSS because of this
naming inconsistency between _parse-breakpoint (actually a thing) and
parse-breakpoint (not a thing).

Change-Id: I88e1747474213da6c18f277624f842c748690478
Reviewed-on: http://gerrit.causes.com/40951
Reviewed-by: Joe Lencioni <joe.lencioni@brigade.com>
Tested-by: Tom Dooner <tom.dooner@brigade.com>