Fix GCR reference (GoogleCloudPlatform#283)

Author: Takashi Matsuo

endpoints/getting-started/composer.json

@@ -7,8 +7,7 @@
     "require-dev": {
         "google/cloud-tools": "^0.6",
         "symfony/browser-kit": " ^3.0",
-        "paragonie/random_compat": " ^2.0",
-        "monolog/monolog": " ^1.19"
+        "paragonie/random_compat": " ^2.0"
     },
     "autoload": {
         "psr-4": {