Fix write image is async

Author: German Lena

index.js

@@ -29,7 +29,7 @@ async function run(params) {
 
     process(output, image, params)
 
-    output.build(params);
+    await output.build(params);
   } catch (e) {
     logger.error(e);
   }

lib/output/gcode.js

@@ -113,8 +113,9 @@ module.exports = class Gcode {
     }
   }
 
-  build({outputFilename, filename}) {
+  async build({outputFilename, filename}) {
     const file = outputFilename ? outputFilename : `./${filename}.gcode`;
     fs.writeFileSync(file, this.code.join("\n"));
+    return Promise.resolve();
   }
 };

lib/output/previewer.js

@@ -56,8 +56,13 @@ module.exports = class Previewer {
     this.laserStatus = false;
   }
 
-  build({outputFilename, filename}) {
+  async build({outputFilename, filename}) {
     const file = outputFilename ? outputFilename : `./preview.${filename}`;
-    this.image.write(file);
+    return new Promise((resolve, reject) => {
+      this.image.write(file, (err) => {
+        if (err) { return reject(err); }
+        resolve();
+      });
+    });
   }
 };