Fixing compatibility with linux os

Thank you, Travis! Turns out the cairo gem isn't perfectly the same in Linux...

spec/graphics/graphics_images_spec.rb

@@ -21,7 +21,7 @@ describe Squib::Card do
 
   context '#png' do
     it 'makes all the expected calls on a smoke test' do
-      expect(@context).to receive(:antialias=).with('best')
+      expect(@context).to receive(:antialias=).with('subpixel')
       expect(@context).to receive(:save).once
       expect(@context).to receive(:translate).with(-37, -38).once
       expect(@context).to receive(:rotate).with(0.0).once
@@ -48,7 +48,7 @@ describe Squib::Card do
     it 'makes all the expected calls on a smoke test' do
       expect(@svg).to receive(:width).and_return(100).twice
       expect(@svg).to receive(:height).and_return(100).twice
-      expect(@context).to receive(:antialias=).with('best').once
+      expect(@context).to receive(:antialias=).with('subpixel').once
       expect(@context).to receive(:save).once
       expect(@context).to receive(:rotate).with(0.0).once
       expect(@context).to receive(:translate).with(37, 38).once

spec/graphics/graphics_shapes_spec.rb

@@ -23,7 +23,7 @@ describe Squib::Card do
 
   context 'rect' do
     it 'make all the expected calls on a smoke test' do
-      expect(@context).to receive(:antialias=).with('best')
+      expect(@context).to receive(:antialias=).with('subpixel')
       expect(@context).to receive(:save).once
       expect(@context).to receive(:rounded_rectangle).with(37, 38, 50, 100, 10, 15).twice
       expect_stroke('#fff', '#f00', 2.0)
@@ -38,7 +38,7 @@ describe Squib::Card do
 
   context 'circle' do
     it 'make all the expected calls on a smoke test' do
-      expect(@context).to receive(:antialias=).with('best')
+      expect(@context).to receive(:antialias=).with('subpixel')
       expect(@context).to receive(:save).once
       expect(@context).to receive(:move_to).with(137, 38)
       expect(@context).to receive(:circle).with(37, 38, 100).twice
@@ -54,7 +54,7 @@ describe Squib::Card do
 
   context 'triangle' do
     it 'make all the expected calls on a smoke test' do
-      expect(@context).to receive(:antialias=).with('best')
+      expect(@context).to receive(:antialias=).with('subpixel')
       expect(@context).to receive(:save).once
       expect(@context).to receive(:triangle).with(1, 2, 3, 4, 5, 6).twice
       expect_stroke('#fff', '#f00', 2.0)
@@ -67,7 +67,7 @@ describe Squib::Card do
 
   context 'line' do
     it 'make all the expected calls on a smoke test' do
-      expect(@context).to receive(:antialias=).with('best')
+      expect(@context).to receive(:antialias=).with('subpixel')
       expect(@context).to receive(:save).once
       expect(@context).to receive(:move_to).with(1, 2).once
       expect(@context).to receive(:line_to).with(3, 4).once

spec/graphics/graphics_text_spec.rb

@@ -20,7 +20,7 @@ describe Squib::Card, '#text' do
     it 'make all the expected calls on a smoke test' do
       extent = Pango::Rectangle.new(50,60,100,200)
       expect(Squib.logger).to receive(:debug).once
-      expect(context).to receive(:antialias=).with('best').once
+      expect(context).to receive(:antialias=).with('subpixel').once
       expect(context).to receive(:save).once
       expect(context).to receive(:set_source_color).once
       expect(context).to receive(:move_to).with(10, 15).once