Fixes Cairo-enabled build breakage from "Add C++17 compatibility in a…

…ddition to C++11 (adobe#194)" commit

Commit e091851 missed a change in the cairo-related code.

Fixes adobe#195.

svgnative/src/ports/cairo/CairoSVGRenderer.cpp

@@ -304,7 +304,7 @@ inline void createCairoPattern(const Paint& paint, float opacity, cairo_pattern_
 {
     *pat = NULL;
 
-    if (paint.type() != typeid(Gradient))
+    if (!SVGNative::holds_alternative<Gradient>(paint))
         return;
 
     const auto& gradient = SVGNative::get<Gradient>(paint);