Adds a hook before MSICreator.create() is called (electron#623)

This allows users to take advantage of the template configuration that electron-wix-msi provdes (see https://github.com/felixrieseberg/electron-wix-msi#template-configuration-optional for details)

trailing whitespace removal

packages/maker/wix/src/Config.ts

@@ -1,3 +1,5 @@
+import { MSICreator } from 'electron-wix-msi/lib/creator';
+
 export interface MakerWixConfig {
   /**
    * String to set as appUserModelId on the shortcut. If none is passed, it'll
@@ -68,6 +70,10 @@ export interface MakerWixConfig {
    * The password to decrypt the certificate given in `certificateFile`.
    */
   certificatePassword?: string;
+  /**
+   * Allows for the modification of the MSICreator before create is called.
+   */
+  beforeCreate?: (creator: MSICreator) => Promise<void> | void;
 }
 export interface UIOptions {
   /**

packages/maker/wix/src/MakerWix.ts

@@ -38,6 +38,9 @@ export default class MakerWix extends MakerBase<MakerWixConfig> {
       outputDirectory: outPath,
     }) as MSICreatorOptions);
 
+    if (this.config.beforeCreate) {
+      await Promise.resolve(this.config.beforeCreate(creator));
+    }
     await creator.create();
     const { msiFile } = await creator.compile();