Core: Use charAt instead of array notation on strings, to support IE8(?)

Closes jquery-validation#1067

Author: NetImperia

src/core.js

@@ -617,7 +617,7 @@ $.extend($.validator, {
 		// specified in the element's HTML5 data attribute
 		// return the generic message if present and no method specific message is present
 		customDataMessage: function( element, method ) {
-			return $( element ).data( "msg" + method[ 0 ].toUpperCase() +
+			return $( element ).data( "msg" + method.charAt( 0 ).toUpperCase() +
 				method.substring( 1 ).toLowerCase() ) || $( element ).data("msg");
 		},
 
@@ -922,7 +922,7 @@ $.extend($.validator, {
 		var method, value,
 			rules = {}, $element = $( element );
 		for ( method in $.validator.methods ) {
-			value = $element.data( "rule" + method[ 0 ].toUpperCase() + method.substring( 1 ).toLowerCase() );
+			value = $element.data( "rule" + method.charAt( 0 ).toUpperCase() + method.substring( 1 ).toLowerCase() );
 			if ( value !== undefined ) {
 				rules[ method ] = value;
 			}