Use env var to specify path to npm binary

script/vsts/platforms/macos.yml

@@ -19,11 +19,12 @@ jobs:
   - script: npm install --global npm@6.2.0
     displayName: Update npm
 
-  - script: export PATH="/usr/local/bin:${PATH}" && script/bootstrap
+  - script: script/bootstrap
     displayName: Bootstrap build environment
     env:
       CI: true
       CI_PROVIDER: VSTS
+      NPM_BIN_PATH: /usr/local/bin/npm
 
   - script: script/lint
     displayName: Run linter