Run npm install instead of npm ci.

Due to unexpected os dependency of lib fs-events.

gulpfile.js

@@ -97,7 +97,7 @@ function npm_install_contracts(cb) {
         return cb();
     }
 
-    exec('npm ci', (error, stdout, stderr) => {
+    exec('npm install', (error, stdout, stderr) => {
         if (error) {
             console.error(stderr);
             throw error;