refactor($sniffer): avoid unnecessary call to substring

src/ng/sniffer.js

@@ -36,7 +36,7 @@ function $SnifferProvider() {
       for (var prop in bodyStyle) {
         if (match = vendorRegex.exec(prop)) {
           vendorPrefix = match[0];
-          vendorPrefix = vendorPrefix.substr(0, 1).toUpperCase() + vendorPrefix.substr(1);
+          vendorPrefix = vendorPrefix[0].toUpperCase() + vendorPrefix.substr(1);
           break;
         }
       }