Added href to SVGAttributes<T>

According to MDN, `xlink:href` has been deprecated. The recommendation is to use `href` (without the namespace prefix) instead. 
Source: https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/xlink:href

types/react/v15/index.d.ts

@@ -3028,6 +3028,7 @@ declare namespace React {
         hanging?: number | string;
         horizAdvX?: number | string;
         horizOriginX?: number | string;
+        href?: string;
         ideographic?: number | string;
         imageRendering?: number | string;
         in2?: number | string;