The current regexp simply matches the first occurence, which more often than
not points to the *previous* variable.
* etc/snippets/text-mode/guix-commit-message-update-package ($1): Restrict
match to beginning of line with optional indentation.
* etc/snippets/text-mode/guix-commit-message-update-package: Since git commit
mode is not derived from any Lisp mode, so-called sexp or symbols do not
include the period character. As a consequence, names including versions are
not properly extracted. Also use more idiomatic (goto-char (point-min))
instead of (beginning-of-buffer).
