update build process for docs

build/build-docs.js

@@ -0,0 +1,8 @@
+// https://github.com/shelljs/shelljs
+const shell = require('shelljs');
+
+shell.exec('gitbook build', (code, stdout, stderr) => {
+  if( code === 0 ) {
+    shell.exec('mv _book site/docs')
+  }
+});