Fix checked mode test

TBR=ricow@google.com
BUG=

Review URL: https://codereview.chromium.org//920823002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@43727 260f80e4-7a28-3924-810f-c04153c831b5

tests/standalone/io/platform_test.dart

@@ -68,7 +68,7 @@ testIsolate() {
 
 
 testVersion() {
-  checkValidVersion(string version) {
+  checkValidVersion(String version) {
     RegExp re = new RegExp(r'(\d+)\.(\d+)\.(\d+)(-dev\.([^\.]*)\.([^\.]*))?');
     var match = re.firstMatch(version);
     Expect.isNotNull(match);