fix(tools): simplify syntax with a ternary

Author: zeroedin

tools/pfe-tools/custom-elements-manifest/lib/Manifest.ts

@@ -319,15 +319,9 @@ export class Manifest {
       // split the demoSource into an array of parts
       const demoSourceParts = demoSource.split('/');
       // if demoSourceParts contains options.elementsDir, then build the filePath from the rootDir and the demoSource
-      let filePath;
-      if (demoSourceParts.includes(options.elementsDir)) {
-        filePath =
-          path.normalize(path.posix.join(options.rootDir, demoSource));
-      // otherwise, build the filePath from the rootDir, options.elementsDir, and the demoSource
-      } else {
-        filePath =
-          path.normalize(path.posix.join(options.rootDir, options.elementsDir, demoSource));
-      }
+      const filePath = demoSourceParts.includes(options.elementsDir) ?
+            path.normalize(path.posix.join(options.rootDir, demoSource))
+          : path.normalize(path.posix.join(options.rootDir, options.elementsDir, demoSource));
       const [last = ''] = filePath.split(path.sep).reverse();
       const filename = last.replace('.html', '');
       const isMainElementDemo = filename === 'index';