Formatting: formally declared variable before use in CPColor.j

Variable `isVertical` is used throughout the function
`patternColorsFromPattern` in CPColor.j despite never being declared.
In this pull request, the variable is declared formally in the variable
list before its use.

AppKit/CPColor.j

@@ -1247,7 +1247,8 @@ var patternColorsFromPattern = function(pattern, attributes, imageFactory)
             bottomHeight,
             centerWidthHeight,
             centerIsNil,
-            numParts;
+            numParts,
+            isVertical;
 
         // positions are mandatory
         if (pattern.indexOf("{position}") < 0)