Gulp Build Fails

[kns94]

When I try to build gulp, I get the following error message:

var stylesheetMap = new Map();
^
ReferenceError: Map is not defined
at restructBlock (/home/kshah/Desktop/angular-templates/versatile-dashboard-theme/node_modules/gulp-csso/node_modules/csso/lib/compressor/restructure/4-restructShorthand.js:320:29)
at module.exports (/home/kshah/Desktop/angular-templates/versatile-dashboard-theme/node_modules/gulp-csso/node_modules/csso/lib/compressor/restructure/index.js:88:5)
at compressBlock (/home/kshah/Desktop/angular-templates/versatile-dashboard-theme/node_modules/gulp-csso/node_modules/csso/lib/compressor/index.js:98:9)
at compress (/home/kshah/Desktop/angular-templates/versatile-dashboard-theme/node_modules/gulp-csso/node_modules/csso/lib/compressor/index.js:125:28)
at Object.minify (/home/kshah/Desktop/angular-templates/versatile-dashboard-theme/node_modules/gulp-csso/node_modules/csso/lib/index.js:56:9)
at Transform.stream._transform (/home/kshah/Desktop/angular-templates/versatile-dashboard-theme/node_modules/gulp-csso/index.js:23:34)
at Transform._read (_stream_transform.js:179:10)
at Transform._write (_stream_transform.js:167:12)
at doWrite (_stream_writable.js:223:10)
at writeOrBuffer (_stream_writable.js:213:5)