match sip binding of QgsSymbolV2::renderHints() to c++ interface

Author: jef-n

python/core/symbology-ng-core.sip

@@ -740,7 +740,7 @@ public:
     void setAlpha( qreal alpha );
 
     //! @note added in 1.5
-    int renderHints() const;
+    int renderHints();
     //! @note added in 1.5
     void setRenderHints( int hints );