feat: add ElectronVersions.fetch()

Add a public method to explicitly fetch a new version list.

Previously, it would check to see if the cache was too old but there
was no explicit way to fetch new versions on demand. This feature is
needed for Electron Fiddle's "Update Electron Release List" button.

Author: ckerr

src/versions.ts

@@ -240,18 +240,12 @@ export class ElectronVersions extends BaseVersions {
     return new ElectronVersions(versionsCache, now, versions);
   }
 
-  // upate the cache if it's too old
-  private async keepFresh(): Promise<void> {
-    const d = debug('fiddle-core:ElectronVersions:keepFresh');
-
-    // if it's still fresh, do nothing
+  // update the cache
+  public async fetch(): Promise<void> {
+    const d = debug('fiddle-core:ElectronVersions:fetch');
     const { mtimeMs, versionsCache } = this;
-    const now = Date.now();
-    if (ElectronVersions.isCacheFresh(mtimeMs, now)) return;
-
-    // update the cache
     try {
-      this.mtimeMs = now;
+      this.mtimeMs = Date.now();
       const versions = await ElectronVersions.fetchVersions(versionsCache);
       this.setVersions(versions);
       d(`saved "${versionsCache}"`);
@@ -261,6 +255,13 @@ export class ElectronVersions extends BaseVersions {
     }
   }
 
+  // upate the cache iff it's too old
+  private async keepFresh(): Promise<void> {
+    if (!ElectronVersions.isCacheFresh(this.mtimeMs, Date.now())) {
+      await this.fetch();
+    }
+  }
+
   public override get prereleaseMajors(): number[] {
     void this.keepFresh();
     return super.prereleaseMajors;