Fix Salesforce Web "Unhandled 'error' event" build error with Node.js 6.5

build-with-tests:
     [echo] build and test
     [exec] (node:5959) fs: re-evaluating native module sources is not supported. If you are using the graceful-fs module, please update it to a more recent version.
     [exec] [15:39:32] Using gulpfile ~/ws/nuxeo-new/addons/nuxeo-salesforce/nuxeo-salesforce-web/gulpfile.js
     [exec] [15:39:32] Starting 'clean'...
     [exec] [15:39:32] Finished 'clean' after 11 ms
     [exec] [15:39:32] Starting 'default'...
     [exec] [15:39:32] Starting 'copy'...
     [exec] [15:39:32] Starting 'styles'...
     [exec] [15:39:33] styles all files 901 B
     [exec] [15:39:33] Finished 'styles' after 667 ms
     [exec] [15:39:34] copy all files 13.16 MB
     [exec] [15:39:34] Finished 'copy' after 1.5 s
     [exec] [15:39:34] Starting 'elements'...
     [exec] [15:39:34] Finished 'elements' after 5.45 ms
     [exec] [15:39:34] Starting 'images'...
     [exec] [15:39:34] Starting 'fonts'...
     [exec] [15:39:34] Starting 'html'...
     [exec] (node:5959) fs: re-evaluating native module sources is not supported. If you are using the graceful-fs module, please update it to a more recent version.
     [exec] [15:39:34] Starting 'compress'...
     [exec] [15:39:34] Finished 'fonts' after 295 ms
     [exec] [15:39:34] gulp-cssmin: Skipping unsupported css scripts/vendor/json2.js
     [exec] [15:39:34] gulp-cssmin: Skipping unsupported css scripts/app.js
     [exec] 
     [exec] events.js:160
     [exec]       throw er; // Unhandled 'error' event
     [exec]       ^
     [exec] Error
     [exec]     at new JS_Parse_Error (eval at <anonymous> (/home/anahide/ws/nuxeo-new/addons/nuxeo-salesforce/nuxeo-salesforce-web/node_modules/gulp-uglify/node_modules/uglify-js/tools/node.js:22:1), <anonymous>:1526:18)
     [exec]     at js_error (eval at <anonymous> (/home/anahide/ws/nuxeo-new/addons/nuxeo-salesforce/nuxeo-salesforce-web/node_modules/gulp-uglify/node_modules/uglify-js/tools/node.js:22:1), <anonymous>:1534:11)
     [exec]     at croak (eval at <anonymous> (/home/anahide/ws/nuxeo-new/addons/nuxeo-salesforce/nuxeo-salesforce-web/node_modules/gulp-uglify/node_modules/uglify-js/tools/node.js:22:1), <anonymous>:2025:9)
     [exec]     at token_error (eval at <anonymous> (/home/anahide/ws/nuxeo-new/addons/nuxeo-salesforce/nuxeo-salesforce-web/node_modules/gulp-uglify/node_modules/uglify-js/tools/node.js:22:1), <anonymous>:2033:9)
     [exec]     at unexpected (eval at <anonymous> (/home/anahide/ws/nuxeo-new/addons/nuxeo-salesforce/nuxeo-salesforce-web/node_modules/gulp-uglify/node_modules/uglify-js/tools/node.js:22:1), <anonymous>:2039:9)
     [exec]     at semicolon (eval at <anonymous> (/home/anahide/ws/nuxeo-new/addons/nuxeo-salesforce/nuxeo-salesforce-web/node_modules/gulp-uglify/node_modules/uglify-js/tools/node.js:22:1), <anonymous>:2059:43)
     [exec]     at simple_statement (eval at <anonymous> (/home/anahide/ws/nuxeo-new/addons/nuxeo-salesforce/nuxeo-salesforce-web/node_modules/gulp-uglify/node_modules/uglify-js/tools/node.js:22:1), <anonymous>:2239:73)
     [exec]     at eval (eval at <anonymous> (/home/anahide/ws/nuxeo-new/addons/nuxeo-salesforce/nuxeo-salesforce-web/node_modules/gulp-uglify/node_modules/uglify-js/tools/node.js:22:1), <anonymous>:2112:19)
     [exec]     at eval (eval at <anonymous> (/home/anahide/ws/nuxeo-new/addons/nuxeo-salesforce/nuxeo-salesforce-web/node_modules/gulp-uglify/node_modules/uglify-js/tools/node.js:22:1), <anonymous>:2072:24)
     [exec]     at eval (eval at <anonymous> (/home/anahide/ws/nuxeo-new/addons/nuxeo-salesforce/nuxeo-salesforce-web/node_modules/gulp-uglify/node_modules/uglify-js/tools/node.js:22:1), <anonymous>:2819:23)
     [exec] [15:39:35] gulp-cssmin: Skipping unsupported css bower_components/webcomponentsjs/webcomponents-lite.min.js
     [exec] [15:39:35] Finished 'compress' after 682 ms