[fbsync] Proper error message (#3725)

Summary:
* Proper error message

Now when there are missing ffmpeg libraries the error displayed is:
```
{0} header files were not found, disabling ffmpeg.
```
This is because the missing `.format`.

This PR fixes the warning message by appending the proper format operation.

* Use f-string

Reviewed By: NicolasHug

Differential Revision: D28169143

fbshipit-source-id: 205f5467c92a9d5d930d6e28e20ba9b02980120b

Co-authored-by: Prabhat Roy <[email protected]>

Author: 2 people

setup.py

@@ -374,8 +374,7 @@ def get_extensions():
                 library_found |= len(glob.glob(full_path)) > 0
 
             if not library_found:
-                print('{0} header files were not found, disabling ffmpeg '
-                      'support')
+                print(f'{library} header files were not found, disabling ffmpeg support')
                 has_ffmpeg = False
 
     if has_ffmpeg: