Update CI config (#130)

Author: dpebot

.kokoro/samples-test.sh

@@ -24,6 +24,11 @@ export GCLOUD_PROJECT=long-door-651
 
 cd $(dirname $0)/..
 
+# Run a pre-test hook, if a pre-samples-test.sh is in the project
+if [ -f .kokoro/pre-samples-test.sh ]; then
+    . .kokoro/pre-samples-test.sh
+fi
+
 npm install
 
 # Install and link samples

.kokoro/test.bat

@@ -17,6 +17,8 @@
 cd /d %~dp0
 cd ..
 
+call npm install -g npm@5 || goto :error
+
 call npm install || goto :error
 call npm run test || goto :error