Remove gulp global install step from Azure pipeline (#1115)

* Remove gulp global install step

* Prefix each npm command with 'call'

azure-pipelines.yml

@@ -21,9 +21,6 @@ steps:
     versionSpec: '10.x'
   displayName: 'Install Node.js'
 
-- script: npm install -g gulp
-  displayName: 'Global install gulp'
-
 - powershell: |
     choco install cloc --no-progress
     cloc --include-lang TypeScript,JavaScript,HTML,Sass,CSS --vcs git
@@ -31,11 +28,11 @@ steps:
 
 - script: |
     node --version
-    npm --version
+    call npm --version
   displayName: 'Version checks'
 
-- script: npm install
+- script: call npm install
   displayName: 'npm install'
 
-- script: npm run build
+- script: call npm run build
   displayName: 'npm run build'