update composer installing protobuf v3 for php-qps
diff --git a/src/php/tests/qps/composer.json b/src/php/tests/qps/composer.json
index 8c1e7b6..f851264 100644
--- a/src/php/tests/qps/composer.json
+++ b/src/php/tests/qps/composer.json
@@ -1,8 +1,7 @@
 {
-  "minimum-stability": "dev",
   "require": {
     "grpc/grpc": "dev-master",
-    "google/protobuf": "^v3.3.0"
+    "google/protobuf": "v3.4.1"
   },
   "autoload": {
     "psr-4": {