Fixup message

`files.length == 0` means the input was empty, so including it in the
message just added confusing whitespace, as well as broke the grammar of
the sentence.

src/main.ts

@@ -63,7 +63,7 @@ async function run() {
     if (config.input_files) {
       const files = paths(config.input_files);
       if (files.length == 0) {
-        console.warn(`🤔 ${config.input_files} not include valid file.`);
+        console.warn(`🤔 no assets to upload.`);
       }
       const currentAssets = rel.assets;
       const assets = await Promise.all(