* Fix some caching issues

.travis.yml

@@ -1,5 +1,11 @@
 language: php
 
+dist: trusty
+matrix:
+  include:
+    - php: 5.3
+      dist: precise
+
 php:
   - 5.3
   - 5.4

lib/Providers/Time/ConvertUnixTimeDotComTimeProvider.php

@@ -6,7 +6,7 @@ class ConvertUnixTimeDotComTimeProvider implements ITimeProvider
 {
     public function getTime() {
         $json = @json_decode(
-            @file_get_contents('http://www.convert-unix-time.com/api?timestamp=now')
+            @file_get_contents('http://www.convert-unix-time.com/api?timestamp=now&r=' . uniqid(null, true))
         );
         if ($json === null || !is_int($json->timestamp))
             throw new \TimeException('Unable to retrieve time from convert-unix-time.com');

lib/Providers/Time/HttpTimeProvider.php

@@ -26,7 +26,8 @@ class HttpTimeProvider implements ITimeProvider
                     'request_fulluri' => true,
                     'header' => array(
                         'Connection: close',
-                        'User-agent: TwoFactorAuth HttpTimeProvider (https://github.com/RobThree/TwoFactorAuth)'
+                        'User-agent: TwoFactorAuth HttpTimeProvider (https://github.com/RobThree/TwoFactorAuth)',
+                        'Cache-Control: no-cache'
                     )
                 )
             );