Fix package-buffer-info() complains "lacks a file header"

[sunlin7]

Hi,
The (package-buffer-info) complains "lacks a file header", here is the backtrace:

Installing packages ..
Debugger entered -- Lisp error: (error "Package lacks a file header")
signal(error ("Package lacks a file header"))
error ("Package lacks a file header")
package-buffer-info()
quelpa-get-package-desc("~/.emacs.d/quelpa/packages/uv.el")

This PR add the .el on head line to satisfy emacs' requirement.
Please approve it. Thank you!

[johannes-mueller]

Thanks, merging.

[sunlin7]

Thank you!