Set $current-bp and $counter in global scope

Due to sass/sass#1474, functions such as fluid() fail, returning NaN or Infinity because the global $current-bp var is not set.

Author: cazzerson

breakpoint/_core.scss

@@ -30,15 +30,15 @@ $first-breakpoint: append($first-breakpoint, ());
         // normalize quotes
         $label: quote(unquote($label));
 
-        $counter: $counter + 1;
+        $counter: $counter + 1 !global;
 
         // push label to label list names = push(names, myname)
         $first-breakpoint: append($first-breakpoint, $label, comma);
 
     }
 
     // set current breakpoint for fluid function
-    $current-bp: $min;
+    $current-bp: $min !global;
 
     // min width mq
     @if ($min and $max == false) {