Clear out the build directory before compiling lang.

scripts/format-lang.js

@@ -1,11 +1,19 @@
 const fs = require('fs');
 const path = require('path');
+const del = require('del');
 const prettier = require('prettier');
+const chalk = require('chalk');
 
 const src = path.resolve(__dirname, '../lang');
 const dest = path.resolve(__dirname, '../build');
 const files = fs.readdirSync(src);
 
+const removed = del.sync([path.join(dest, '*.json')]);
+
+if (removed.length) {
+  console.log(removed.map(n => `${n} ${chalk.redBright('✗')}`).join('\n'));
+}
+
 if (!fs.existsSync(dest)) {
   fs.mkdirSync(dest);
 }
@@ -23,5 +31,5 @@ files.forEach(file => {
 
   fs.writeFileSync(path.resolve(dest, file), json);
 
-  console.log(path.resolve(src, file), '->', path.resolve(dest, file));
+  console.log(path.resolve(src, file), chalk.greenBright('->'), path.resolve(dest, file));
 });