Add well-known timestamps to JSON for PHP (#3564)

diff --git a/conformance/conformance_php.php b/conformance/conformance_php.php
index b6e12c0..2e3f783 100755
--- a/conformance/conformance_php.php
+++ b/conformance/conformance_php.php
@@ -38,6 +38,10 @@
 
 use  \Conformance\WireFormat;
 
+if (!ini_get("date.timezone")) {
+  ini_set("date.timezone", "UTC");
+}
+
 $test_count = 0;
 
 function doTest($request)