showcase: use correct width&height vars

Fixes #179

lib/squib/card.rb

@@ -52,7 +52,11 @@ module Squib
     end
 
     def finish!
-      @cairo_surface.finish
+      begin
+        @cairo_surface.finish
+      rescue Cairo::SurfaceFinishedError
+        # do nothin - if it's already finished that's fine
+      end
     end
 
     ########################

lib/squib/graphics/showcase.rb

@@ -33,7 +33,7 @@ module Squib
     # :nodoc:
     # @api private
     def trim_rounded(src, trim, radius)
-      trim_cc = Cairo::Context.new(Cairo::ImageSurface.new(src.width - 2.0 * trim, src.height - 2.0 * trim))
+      trim_cc = Cairo::Context.new(Cairo::ImageSurface.new(@width - 2.0 * trim, @height - 2.0 * trim))
       trim_cc.rounded_rectangle(0, 0, trim_cc.target.width, trim_cc.target.height, radius, radius)
       trim_cc.set_source(src, -1 * trim, -1 * trim)
       trim_cc.clip

lib/squib/version.rb

@@ -6,5 +6,5 @@ module Squib
   # Most of the time this is in the alpha of the next release.
   # e.g. v0.0.5a is on its way to becoming v0.0.5
   #
-  VERSION = '0.12.0a'
+  VERSION = '0.12.0b'
 end