fix a glitch on blur transition effect

As described issue #174

src/sass/transitions/blur.sass

@@ -5,12 +5,12 @@
 .vegas-transition-blur,
 .vegas-transition-blur2
     opacity: 0
-    filter: blur($vegas-blur-value)
+    filter: blur($vegas-blur-value) brightness(1.01);
 
 .vegas-transition-blur-in,
 .vegas-transition-blur2-in
     opacity: 1
-    filter: blur(0px)
+    filter: blur(0px) brightness(1.01);
 
 .vegas-transition-blur2-out
-    opacity: 0
+    opacity: 0