Revert "Removed the @Override annotation as it resulted in a compilation error."

This reverts commit 4aa6256487.

src/main/java/org/scribe/extractors/JsonTokenExtractor.java

@@ -10,6 +10,7 @@ public class JsonTokenExtractor implements AccessTokenExtractor
 {
   private Pattern accessTokenPattern = Pattern.compile("\"access_token\":\\s*\"(\\S*?)\"");
 
+  @Override
   public Token extract(String response)
   {
     Preconditions.checkEmptyString(response, "Cannot extract a token from a null or empty String");