No need to specify the env var explicitly

CONTRIBUTING.md

@@ -19,7 +19,7 @@ In order to protect both you and ourselves, you will need to sign the
 The basic build script should run to completion.
 
 ```sh
-$ MASTER=1 ./scripts/kokoro.sh
+$ ./scripts/kokoro.sh
 ```
 
 More details to come.

kokoro/master.cfg

@@ -1,5 +1 @@
 build_file: "grpc-web/scripts/kokoro.sh"
-env_vars {
-  key: "MASTER"
-  value: "1"
-}

scripts/kokoro.sh

@@ -17,6 +17,8 @@ set -ex
 SCRIPT_DIR=$(dirname "$0")
 cd "${SCRIPT_DIR}"
 
+export MASTER=1
+
 ./run_basic_tests.sh
 
 ./run_interop_tests.sh