fix charset from utf8 to utf-8

Author: Amin Cheloh

AndroidAsync/src/com/koushikdutta/async/http/body/UrlEncodedFormBody.java

@@ -59,7 +59,7 @@ public void write(AsyncHttpRequest request, final DataSink response, final Compl
     public static final String CONTENT_TYPE = "application/x-www-form-urlencoded";
     @Override
     public String getContentType() {
-        return CONTENT_TYPE + "; charset=utf8";
+        return CONTENT_TYPE + "; charset=utf-8";
     }
 
     @Override

AndroidAsync/src/com/koushikdutta/async/http/server/AsyncHttpServerResponseImpl.java

@@ -206,13 +206,13 @@ public void send(String string) {
         responseCode(200);
         String contentType = mRawHeaders.get("Content-Type");
         if (contentType == null)
-            contentType = "text/html; charset=utf8";
+            contentType = "text/html; charset=utf-8";
         send(contentType, string);
     }
 
     @Override
     public void send(JSONObject json) {
-        send("application/json; charset=utf8", json.toString());
+        send("application/json; charset=utf-8", json.toString());
     }
 
     @Override